The opinion
United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued December 11, 2025 Decided August 25, 2026
No. 25-5137
NORWICH PHARMACEUTICALS, INC.,
APPELLANT
v.
ROBERT F. KENNEDY, JR., IN HIS OFFICIAL CAPACITY AS
SECRETARY OF HEALTH AND HUMAN SERVICES, ET AL.,
APPELLEES
Appeal from the United States District Court
for the District of Columbia
(No. 1:25-cv-00091)
Andrew D. Prins argued the cause for appellant. With
him on the briefs were Rachael Westmoreland, Lia R. Barrett,
Matthew S. Murphy, and Nicholas L. Schlossman. Margaret
Dotzel entered an appearance.
Gabriel Schonfeld, Attorney, U.S. Department of Justice,
argued the cause for federal appellees. With him on the brief
were Brett A. Shumate, Assistant Attorney General, and Daniel
Tenny, Attorney. Joshua Dos Santos and Benjamin C. Wei,
Attorneys, entered appearances.
Bryan M. Killian argued the cause for appellee Salix
Pharmaceuticals, Inc. With him on the brief were Douglas A.
2
Hastings, Brendan J. Anderson, Michael Abernathy, and
Wan-Shon Lo. Colin S. Harris entered an appearance.
Brian T. Burgess argued the cause for appellee Teva
Pharmaceuticals USA, Inc. With him on the brief was Sierra
Perez-Sparks.
Before: PILLARD, WALKER, and GARCIA, Circuit Judges.
Opinion for the Court filed by Circuit Judge GARCIA.
GARCIA, Circuit Judge: Under the statutes governing the
FDA’s drug-approval process, the first company to submit a
complete application for a generic version of a drug—thereby
exposing itself to potential patent litigation from the brand-
name drug maker—is typically rewarded with a 180-day period
of marketing exclusivity. No competing generic can be sold
until that period expires. To avoid unwarranted delays in
generics coming to market, Congress also specified that these
“first applicants” forfeit that exclusivity in certain
circumstances. This case presents statutory interpretation
questions about two such provisions, which concern the first
applicant’s “failure to market” or “failure to obtain tentative
approval” from the FDA. We conclude that the FDA correctly
interpreted the first but applied an incorrect causation standard
for the second. We therefore affirm in part, reverse in part,
and remand to the district court with instructions to remand to
the agency for further proceedings.
I
A
The Food, Drug, and Cosmetic Act (FDCA) requires
companies to secure FDA approval before selling “any new
drug.” 21 U.S.C. § 355(a). The new drug application
process is typically “onerous and lengthy,” Mut. Pharm. Co. v.
Bartlett, 570 U.S. 472, 476 (2013), requiring extensive
3
“scientific data showing that the drug is safe and effective,”
Caraco Pharm. Lab’ys, Ltd. v. Novo Nordisk A/S, 566 U.S.
399, 404 (2012). Developers of generic drugs, however, can
submit an Abbreviated New Drug Application (ANDA). Id.
at 404–05. An ANDA “piggy-back[s]” on the “evidence of
safety and efficacy” that supported approval of the brand-name
drug. Id. at 405. This process is “designed to speed the
introduction of low-cost generic drugs to market.” Id. The
FDA generally approves the ANDA so long as the generic is,
essentially, the equivalent of the brand-name version. See
PLIVA, Inc. v. Mensing, 564 U.S. 604, 612 (2011); 21 U.S.C.
§ 355(j)(2)(A). But before that approval is finalized, the
ANDA applicant must address patents associated with the
brand-name drug that its generic might infringe.
Most brand-name drugs are covered by a variety of patents
claiming—that is, asserting legal rights over—the drug itself or
its methods of use. When a generic-drug applicant submits an
ANDA, it identifies the brand-name drug its generic mimics
and makes “certification[s]” as to each of the patents associated
with that brand-name product. 21 U.S.C. § 355(j)(2)(A)(i),
(vii). These certifications are identified by the paragraph
numbers in Section 355(j)(2)(A)(vii) of the FDCA. As
relevant here, a Paragraph IV certification attests that a patent
covering the brand-name drug or a use of that drug “is invalid
or will not be infringed” by the generic version. Id.
§ 355(j)(2)(A)(vii)(IV).
As an alternative to these certifications, the generic
manufacturer can “submit a so-called section viii statement,
which asserts that the generic manufacturer will market the
drug for one or more methods of use not covered by the brand’s
patents.” Caraco, 566 U.S. at 406 (citing 21 U.S.C.
§ 355(j)(2)(A)(viii)). If the generic manufacturer relies on a
section viii statement, it “carves out” the patented methods of
4
use from its label and cannot market the drug for those
purposes. Id.
Once the FDA concludes that a generic version is an
adequate equivalent of the brand-name drug, the ANDA’s
certifications determine the effective date of approval. For
example, if an applicant submits only Paragraph I or Paragraph
II certifications, which indicate that patents for the brand-name
drug were not filed or have expired, any approval will be
effective immediately. See 21 U.S.C. § 355(j)(2)(A)(vii)(I)–
(II); id. § 355(j)(5)(B)(i). If an applicant submits an ANDA
with Paragraph IV certifications, by contrast, approval is
delayed to allow the patent holder to sue for patent
infringement. See id. § 355(j)(5)(B)(iii); see also 35 U.S.C.
§ 271(e)(2)(A). If the patent holder sues within a specified
period and that suit is successful, the FDA sets the effective
date of approval for the generic as no earlier than the date the
patent holder’s last valid, infringed patent expires. See 21
U.S.C. § 355(j)(5)(B)(iii)(II)(bb); 35 U.S.C. § 271(e)(4)(A).
In the meantime, the ANDA can only be granted “tentative
approval,” which signifies that an ANDA otherwise meets the
requirements for approval but cannot yet receive final approval
because of a patent issue or, as discussed further below, a
statutory exclusivity period. See 21 U.S.C.
§ 355(j)(5)(B)(iv)(II)(dd)(AA); 21 C.F.R. § 314.105(d).
The infringement suits brought by patent holders in
response to Paragraph IV certifications are costly for the first
generic applicant but can be immensely beneficial to
subsequent generic-makers. If the first generic applicant
proves that the brand-name drug’s patents are invalid, for
instance, the next ANDA submitted for a similar generic might
avoid patent litigation entirely.
To “compensate . . . for research and development costs as
well as the risk of litigation from patent holders,” the statute
5
grants certain “first” applicants submitting an ANDA 180 days
of marketing exclusivity. Teva Pharms., USA, Inc. v. Leavitt,
548 F.3d 103, 104 (D.C. Cir. 2008); see 21 U.S.C.
§ 355(j)(5)(B)(iv). This incentive to be the first generic
applicant “increase[s] competition by expediting the
availability of generic[s].” Teva Pharms. USA, Inc. v.
Sebelius, 595 F.3d 1303, 1305 (D.C. Cir. 2010).
This same benefit can also create opportunities for
anticompetitive practices. Brand and generic companies
could—and, at times, did—collude to have an initial generic
applicant delay its own marketing. And because the
exclusivity period began only once that applicant commenced
marketing, such a delay could in turn postpone market entry for
all subsequent generics. See Teva Pharms., 595 F.3d at 1316–
17, 1317 n.5 (citing Fed. Trade Comm’n, Authorized Generics:
An Interim Report ch. 2, at 1 (2009)). Congress revisited the
first-applicant exclusivity scheme in 2003 to address that risk.
See Medicare Prescription Drug, Improvement, and
Modernization Act of 2003, Pub. L. No. 108-173, 117 Stat.
2066; 149 Cong. Rec. S15746 (daily ed. Nov. 24, 2003)
(statement of Sen. Schumer) (discussing measures to “ensure”
that first-applicant exclusivity “cannot be used as a bottleneck
to prevent additional generic competition”). As part of that
revision, Congress added a series of provisions describing
when the first applicant would “forfeit” its marketing
exclusivity, thereby allowing other generics to enter the
market.
Two of the forfeiture provisions are at issue here.
The first, 21 U.S.C. § 355(j)(5)(D)(i)(I), concerns a failure
to timely market the drug. As relevant here, a first applicant
that submitted its ANDA more than 30 months ago will forfeit
exclusivity if it does not market its drug within 75 days after at
least one of several triggering events has occurred for “each of
6
the patents with respect to which the first applicant submitted
and lawfully maintained a certification qualifying the first
applicant for the 180-day exclusivity period.” Id.
§ 355(j)(5)(D)(i)(I)(bb). These triggering events include: a
final court decision that the patent is invalid or not infringed; a
settlement order or consent decree finding the patent is invalid
or not infringed; or, in certain circumstances, the patent
holder’s withdrawal of patent information previously
submitted to the FDA. Id.; see Teva Pharms., 595 F.3d at
1317.
The second, 21 U.S.C. § 355(j)(5)(D)(i)(IV), concerns a
failure to obtain tentative approval. A first applicant forfeits
exclusivity if the FDA has not tentatively approved that
applicant’s ANDA within 30 months of filing. But the statute
provides an exception that applies if “the failure [to obtain
tentative approval] is caused by a change in or a review of the
requirements for approval . . . imposed after the date on which
the application is filed.” Id.
If either forfeiture event occurs “with respect to” a
particular first applicant, that applicant “shall” forfeit its
marketing exclusivity. Id. § 355(j)(5)(D)(ii).
B
Salix Pharmaceuticals Inc. produces the drug rifaximin
under the brand name Xifaxan. Rifaximin in its 550 mg form
can treat irritable bowel syndrome with diarrhea (IBS-D) and
hepatic encephalopathy (HE), a brain condition caused by
severe liver disease; in its 200 mg form it can treat travelers’
diarrhea. Actavis Laboratories FL, Inc., a wholly owned
subsidiary of Teva Pharmaceuticals USA, Inc., submitted an
ANDA for 550 mg tablets of generic rifaximin on December
18, 2015, the first date any such application was submitted.
Norwich Pharms., Inc. v. Kennedy, 2025 WL 1148463, at *5
(D.D.C. Apr. 18, 2025). Actavis’s ANDA contained various
7
Paragraph IV certifications related to patents for the drug itself,
its use to treat IBS-D, and its use to treat HE. Id.
Salix sued Actavis in March 2016 for patent infringement.
Id. That litigation ended in a September 2018 settlement
under which Actavis admitted its generic would infringe
certain Salix patents, without conceding those patents’ validity.
Id. In exchange, Actavis obtained a license to market either
an authorized generic approved by Salix or its own generic
approved by the FDA no earlier than January 1, 2028. Id.
That date was more than 22 months before the last of the Salix
patents expires. Id. Despite the settlement, Actavis still
needed FDA approval to market its generic version of
rifaximin.
In 2017, just over a year after Actavis submitted its
ANDA, the FDA published a revised draft of its guidance for
rifaximin applications. The guidance recommended that
applicants for the drug conduct additional “dissolution studies”
to show “bioequivalence” with Xifaxan. Id. The FDA gave
final approval to Actavis’s ANDA approximately nine years
later, on March 19, 2026. FDA’s Fed. R. App. P. 28(j) Letter
at 1 (Mar. 19, 2026).
While Actavis’s ANDA remained pending before the
FDA, Norwich Pharmaceuticals, Inc. submitted two ANDAs
for rifaximin generics: No. 214,369 (ANDA ’369) for a 550 mg
dosage and No. 214,370 (ANDA ’370) for a 200 mg dosage.
Salix sued Norwich in March 2020 in the District of Delaware,
alleging that ANDA ’369 infringed several Salix patents,
including No. ’196, which covers features of the drug itself;
No. ’569, which covers the use of rifaximin to treat IBS-D; and
No. ’573, which covers the use of rifaximin to treat HE. See
Compl. ¶¶ 19, 121, 141, Salix Pharms., Ltd. v. Norwich
Pharms., Inc., 2022 WL 3225381 (D. Del. Aug. 10, 2022). By
the end of that case, Salix and Norwich had stipulated that
8
Norwich’s ANDA ’369 and “any amendments or supplements
to [that] ANDA” did not infringe Patent No. ’196. See J.A.
223–24. The Delaware District Court’s final judgment
subsequently determined that Patent No. ’569 for IBS-D was
invalid, but Patent No. ’573—the HE patent—was both valid
and infringed. Salix, 2022 WL 3225381, at *23. The Federal
Circuit affirmed. Salix Pharms., Ltd. v. Norwich Pharms.
Inc., 98 F.4th 1056, 1069–70 (Fed. Cir.), cert. denied, 145 S.
Ct. 567 (2024).1
While that appeal was pending before the Federal Circuit,
Norwich amended its separate ANDA ’370, which previously
addressed only 200 mg rifaximin, to add the 550 mg dosage as
well. As a result of this amendment, Norwich’s ANDA ’370
and Actavis’s ANDA now both contain Paragraph IV
certifications to Patent Nos. ’196 and ’569. But while Actavis
submitted a Paragraph IV certification to the HE patent (No.
’573), Norwich addressed that patent with a section viii
statement asserting it would not market its generic as a
treatment for HE, instead only marketing it as a treatment for
IBS-D.
In January 2025, the FDA concluded that the 550 mg
rifaximin tablets described in Norwich’s ANDA ’370 met the
standard requirements for approval under the FDCA. See
Norwich Pharms., 2025 WL 1148463, at *7, *9. But the FDA
1
The FDA issued only tentative approval for Norwich’s
ANDA ’369. Norwich unsuccessfully challenged that decision.
See Norwich Pharms., Inc. v. Becerra, 703 F. Supp. 3d 1 (D.D.C.
2023), aff’d sub nom. Norwich Pharms., Inc. v. Kennedy, 179 F.4th
48 (D.C. Cir. 2026). In the meantime, Salix has sued Norwich,
alleging that No. ’370 infringes its patents. See Compl. ¶¶ 33–61,
Salix Pharms., Inc. v. Norwich Pharms., Inc., No. 1:24-cv-7140-JFM
(D.N.J. June 20, 2024). A motion for summary judgment is pending
in that litigation.
9
also found that Actavis’s ANDA was eligible for a 180-day
exclusivity period that prevented it from granting Norwich’s
ANDA final approval. Id. at *9. The FDA rejected
Norwich’s arguments that Actavis had forfeited its marketing
exclusivity. Id. at *8–9. The FDA therefore granted
Norwich’s ANDA ’370 only tentative approval. Id. at *9.
C
Norwich filed this suit under the Administrative Procedure
Act, alleging that the FDA’s decision to grant tentative rather
than final approval was arbitrary and capricious and contrary
to law. Norwich also moved for a preliminary injunction.
Salix, the brand-name drug’s producer, and Teva
Pharmaceuticals USA, Inc. (of which Actavis is a wholly
owned subsidiary) intervened in support of the FDA.
According to Norwich, Actavis had forfeited its first-applicant
exclusivity by failing to timely market its generic and to timely
obtain tentative approval from the FDA. At the parties’
request, the district court consolidated consideration of the
motion for a preliminary injunction with its consideration of
the parties’ motions for summary judgment. The court denied
Norwich relief and granted the FDA’s, Teva’s, and Salix’s
cross-motions for summary judgment. Norwich Pharms.,
2025 WL 1148463, at *18.
The court agreed with the FDA that Actavis’s 180-day
exclusivity continued to block final approval of Norwich’s
ANDA No. ’370. Id. at *15. In the court’s view, the “natural
reading” of the statutory text and structure establishes that
triggering events required by the failure to market provision
had not occurred for every “qualifying” patent certification,
notwithstanding Norwich’s HE carveout. Id. at *10–15.
Turning to the failure to obtain tentative approval provision,
the court concluded that Actavis’s failure to obtain such
approval by the statutory deadline was “caused by” the changes
10
in the March 2017 draft product-specific guidance. Id. at *17–
18. The court agreed with the FDA that “caused by” in that
provision did not require that the FDA’s change be a but-for
cause of Actavis’s failure to obtain approval by the deadline.
Id. Norwich appealed.
II
We review the district court’s grant of summary judgment
de novo. AstraZeneca Pharms. LP v. FDA, 713 F.3d 1134,
1138 (D.C. Cir. 2013). We ask, as the district court did, if
there is any genuine dispute of material fact whether the FDA’s
decision was “arbitrary, capricious, an abuse of discretion, or
otherwise not in accordance with law.” Id. at 1138–39
(quoting 5 U.S.C. § 706(2)(A)). When that analysis involves
statutory interpretation disputes, we “exercise [our]
independent judgment” to “decid[e] whether an agency has
acted within its statutory authority.” Loper Bright Enters. v.
Raimondo, 603 U.S. 369, 412 (2024).
Applying those standards, we conclude that the FDA
correctly determined that Actavis has not forfeited its
exclusivity under the “failure to market” provision in 21 U.S.C.
§ 355(j)(5)(D)(i)(I). But the agency applied the wrong
causation standard for the “failure to obtain tentative approval”
provision in 21 U.S.C. § 355(j)(5)(D)(i)(IV). Because of that
error, the FDA must reassess whether Actavis forfeited its
exclusivity under the failure to obtain tentative approval
provision.
As a threshold matter, all agree that unless Actavis
forfeited its exclusivity, its 180-day exclusivity period for
rifaximin 550 mg would block final approval of Norwich’s
ANDA. Norwich’s ANDA contains Paragraph IV
certifications “and is for a drug for which a first applicant
[Actavis] has submitted an application containing such a
certification.” 21 U.S.C. § 355(j)(5)(B)(iv)(I). Norwich
11
spills much ink insisting that Actavis’s certification to the HE
patent could not trigger that exclusivity provision on its own
because Norwich’s ANDA did not include a certification to
that same patent. See Appellant’s Brief 26–37. Actavis
disagrees. Teva’s Brief 37. But we need not decide whether
only “matching” certifications trigger exclusivity under
subparagraph (B)(iv)(I), because there is no dispute that
Norwich’s ANDA contains several certifications “matching”
those in Actavis’s ANDA. The crucial question is instead
whether Actavis has forfeited that exclusivity.
A
We agree with the FDA and the district court that Actavis
has not forfeited its exclusivity by failing to timely market its
generic rifaximin drug.
Under the failure to market provision, a first applicant
forfeits its exclusivity only if a triggering event—such as a final
judicial decision that the patent at issue is invalid or not
infringed—occurs “as to each of the patents with respect to
which the first applicant submitted and lawfully maintained a
certification qualifying the first applicant for the 180-day
exclusivity period.” 21 U.S.C. § 355(j)(5)(D)(i)(I)(bb).
The parties dispute whether Actavis’s “qualifying”
certifications include all Paragraph IV certifications in its
ANDA that made it a first applicant, or only those certifications
that reference the same patents as the Paragraph IV
certifications Norwich included in its later-submitted ANDA
’370. The FDA and Actavis argue the former “all
certifications” view; Norwich urges the latter “matching
certifications” view.
The dispute matters because, in Norwich’s view,
triggering events have occurred for each certification common
12
to the two ANDAs.2 But all agree that no triggering event has
occurred as to the HE patent for which Actavis’s ANDA, but
not Norwich’s, includes a Paragraph IV certification. On
Norwich’s view, that fact is irrelevant because Actavis’s
certification to the HE patent was not “a certification qualifying
the first applicant for the 180-day exclusivity period,” and
Actavis has forfeited its exclusivity period even if no triggering
event has occurred for the HE patent.
We agree with the FDA and Actavis that the statutory
phrase “a certification qualifying the first applicant for the 180-
day exclusivity period” is best read to encompass each of the
Paragraph IV certifications “contain[ed] and lawfully
maintain[ed]” in the first applicant’s ANDA. Accordingly,
Actavis has not forfeited its exclusivity for failure to market
until a triggering event occurs for each patent for which Actavis
included a Paragraph IV certification in its ANDA—including
the HE patent.3
The FDA’s position fits the text of Section
355(j)(5)(D)(i)(I)(bb) and the provisions it references. The
forfeiture provision focuses on the certifications “qualifying
the first applicant for the 180-day exclusivity period under
subparagraph (B)(iv).” To see what makes the first applicant
qualified for—meaning, as the parties agree, eligible for—the
exclusivity period, we look first to the statute’s definition of the
exclusivity period. That provision states that the “180-day
exclusivity period” is “the 180-day period ending on the day
2
Intervenor Salix disputes that assertion. Salix’s Brief 4. We
need not and do not resolve that dispute.
3
No party disputes that Actavis was the first to submit a
substantially complete ANDA for rifaximin 550 mg, nor that its
application “contain[ed] and lawfully maintain[ed]” the Paragraph
IV certifications to Patent Nos. ’196, ’569, and ’573. 21 U.S.C.
§ 355(j)(5)(B)(iv)(II)(bb).
13
before the date on which an application submitted by an
applicant other than a first applicant could become effective
under this clause.” Id. § 355(j)(5)(B)(iv)(II)(aa). Standing
alone, that language does not directly describe what makes an
applicant eligible for marketing exclusivity. But it discusses
that period as a benefit for which only a “first applicant” is
eligible. And the statute defines a “first applicant” as “an
applicant that on the first day on which a substantially complete
application containing a [Paragraph IV certification] is
submitted for approval of a drug, submits a substantially
complete application that contains and lawfully maintains a
[Paragraph IV certification] for the drug.” Id.
§ 355(j)(5)(B)(iv)(II)(bb). That is, a first applicant is one who
submits a substantially complete application before (or at the
same time as) anyone else, with “a [Paragraph IV
certification].” Just one Paragraph IV certification will do the
trick and qualify the applicant as a “first applicant,” and thus,
for the exclusivity period.
Putting that all together: An ANDA applicant qualifies
for the 180-day exclusivity period by being a first applicant for
the drug at issue and qualifies as a first applicant by being the
first to submit and maintain a Paragraph IV certification in a
substantially complete ANDA. As a result, each Paragraph IV
certification in a sufficiently timely and complete ANDA is “a
certification qualifying the first applicant for the 180-day
exclusivity period” for purposes of the failure to market
provision. And a first applicant forfeits exclusivity under that
provision only if a triggering event occurs “as to each” of those
qualifying certifications.
Norwich counters, with some force, that the statutory text
is not so straightforward. For instance, it emphasizes that the
forfeiture provision refers to “a certification qualifying the first
applicant for the 180-day exclusivity period under
subparagraph (B)(iv).” Id. § 355(j)(5)(D)(i)(I)(bb). And if
14
we focus on subparagraph (B)(iv)(I), which describes how the
180-day exclusivity period operates, rather than (B)(iv)(II),
which defines the “180-day exclusivity period” and “first
applicant,” Norwich’s position appears plausible. The
language in subparagraph (B)(iv)(I) is focused on the
perspective of the subsequent application: If that application
“contains a [Paragraph IV] certification . . . and is for a drug
for which a first applicant has submitted an application
containing such a certification,” the subsequent application is
subject to the 180-day exclusivity period. In Norwich’s view,
as previewed above, that “such a certification” language
establishes a “relational” approach under which a first
applicant’s exclusivity period blocks only some subsequent
applications—namely, those with Paragraph IV certifications
to the same patents as the first application. Appellant’s Brief
45–47. That “relational” approach, Norwich says, carries
through to the forfeiture provision: Because the exclusivity
period is “relational” and focused on overlapping certifications,
the forfeiture provision’s reference to those certifications
“qualifying the first applicant for the 180-day exclusivity
period” must be too, and triggering events are therefore
required only for those overlapping certifications. Norwich
also offers accounts of the statute’s history and the drafters’
policy objectives to support its position.
The appellees offer equally plausible rejoinders on these
fronts. But we focus here on one point to which Norwich has
no adequate response and which we find dispositive.
However subparagraph (B)(iv)(I) functions—a question we do
not resolve—the operation of the forfeiture provisions is clear
in one key respect: First applicants are granted a single
exclusivity period that is forfeited as to all subsequent
applicants or not at all. There is no basis in the statute for
Norwich’s suggested “relational” or “partial” forfeiture of
exclusivity. And because only the FDA’s position fits that
feature of the statute, it is the best reading.
15
Per the statute, “[t]he 180-day exclusivity period described
in subparagraph (B)(iv) shall be forfeited by a first applicant if
a forfeiture event occurs with respect to that first applicant.”
21 U.S.C. § 355(j)(5)(D)(ii). This language—as the district
court held and as the FDA, Actavis, and even Norwich
emphasize—describes a single, indivisible exclusivity period:
“The 180-day exclusivity period.” Id. (emphasis added); see
Niz-Chavez v. Garland, 593 U.S. 155, 166 (2021) (“using a
definite article with a singular noun” implies a single, “discrete
thing”). That language, moreover, is focused entirely on the
first applicant, not anything about a subsequent application—
exclusivity is “forfeited by a first applicant” and “with respect
to that first applicant.” The statute then describes a similarly
indivisible consequence of that forfeiture: If “all first
applicants forfeit the 180-day exclusivity period,” then the
exclusivity provisions no longer limit “approval of any
application containing a [Paragraph IV] certification.” 21
U.S.C. § 355(j)(5)(D)(iii). Again, the statute focuses on
whether forfeiture events have occurred as to the first applicant,
and provides that, if so, the applicant will have fully forfeited
the exclusivity period.4
A statute that endorsed Norwich’s view would need to be
written quite differently. On its reading, the statute treats only
those certifications in the first applicant’s ANDA that match a
certification in the subsequent applicant’s ANDA as
4
Indeed, the statute’s forfeiture provisions largely address the
first applicant and the status of its application. See 21 U.S.C.
§ 355(j)(5)(D)(i)(II)–(V) (describing forfeiture when a first applicant
“withdraws” its application, “amends” all qualifying certifications,
“fails to obtain tentative approval,” or “enters into an agreement”).
One forfeiture provision turns on the “expiration of all patents” to
which the first applicant submitted a qualifying certification. Id.
§ 355(j)(5)(D)(i)(VI). None turns on the behavior or certification
strategy of subsequent applicants.
16
“qualifying” certifications. If a triggering event occurred “as
to th[ose] certifications,” then the first applicant would forfeit
its exclusivity as to that subsequent applicant, but not
necessarily as to others. See Reply Brief 10; see also
Appellant’s Brief 46 (“The point of the forfeiture provision is
to forfeit the 180-day exclusivity period under
§ 355(j)(5)(B)(iv)(I) vis-à-vis the subsequent application.”).
Applied here, that would mean that Actavis has forfeited its
exclusivity period with respect to Norwich’s ANDA, but not
with respect to any ANDAs containing a Paragraph IV
certification to the HE patent. The problem for Norwich is
that there is no statutory basis for finding such partial
forfeitures. To support Norwich’s interpretation, instead of
stating that a first applicant forfeits exclusivity “if a forfeiture
event occurs with respect to that first applicant,” 21 U.S.C.
§ 355(j)(5)(D)(ii), the statute would need provisions
establishing that a first applicant can forfeit exclusivity “with
respect to” particular subsequent applicants but retain it as to
others. There are no such provisions.
As a result, we hold that all Paragraph IV certifications
“contain[ed] and lawfully maintain[ed]” in the first applicant’s
ANDA are certifications “qualifying” the first applicant for
exclusivity under Section 355(j)(5)(D)(i)(I)(bb). Because
Actavis’s ANDA included a Paragraph IV certification to the
HE patent, and because there has been no triggering event for
that patent, Actavis has not forfeited exclusivity under the
failure to market provision.
B
Norwich separately argues that the FDA erred in
determining that Actavis did not forfeit its exclusivity by
failing to timely obtain tentative approval for its ANDA.
A first applicant forfeits the exclusivity period if it “fails
to obtain tentative approval of the application within 30 months
17
after the date on which the application is filed, unless the failure
is caused by a change in or a review of the requirements for
approval of the application imposed after the date on which the
application is filed.” 21 U.S.C. § 355(j)(5)(D)(i)(IV).
Actavis’s 30-month deadline was June 18, 2018, at which time
its ANDA had not obtained tentative approval. But the FDA
determined that Actavis had not forfeited its exclusivity
because the statutory exception applied—the delay in approval
was “caused by a change in or a review of the requirements for
approval.” Id. Specifically, the FDA concluded that its draft
guidance for rifaximin ANDAs, released in March 2017, was
“one of the causes” of Actavis’s failure to obtain tentative
approval. Norwich Pharms., 2025 WL 1148463, at *17. The
FDA maintained that “but-for causation” was not required. Id.
We hold that the FDA applied the wrong causation
standard. The exception for failures to obtain tentative
approval “caused by a change in or a review of the
requirements” is best read to apply only if such a change or
review is a but-for cause of the applicant’s failure to timely
obtain tentative approval. We remand for the agency to apply
the correct causal standard in the first instance.5
1
The parties essentially dispute whether, and in what form,
a but-for standard should apply. Under that standard, “an
action ‘is not regarded as a cause of an event if the particular
event would have occurred without it.’” Univ. of Tex. Sw.
Med. Ctr. v. Nassar, 570 U.S. 338, 347 (2013) (quoting W.
Keeton et al., Prosser and Keeton on the Law of Torts 265 (5th
ed. 1984)). Even where the but-for-causation standard
5
Because we agree with Norwich that “caused by” incorporates
a but-for causation analysis, we do not address its argument in the
alternative regarding 21 U.S.C. § 355(q)(1)(G) and Salix’s petition
to the FDA regarding the criteria for rifaximin generics.
18
governs, however, courts sometimes apply an “exception”
when “multiple sufficient causes independently . . . produce a
result.” Paroline v. United States, 572 U.S. 434, 451 (2014)
(quoting Burrage v. United States, 571 U.S. 204, 214 (2014));
see also Dan B. Dobbs, Paul T. Hayden & Ellen M. Bublick,
The Law of Torts § 189 (2d ed. Apr. 2026 update) (explaining
that courts sometimes “drop the but-for test” if “each of two or
more causes is sufficient standing alone to cause the plaintiff’s
harm”).
A simplified example illustrates the difference: If a
baseball game ends 3-0 after the winning team scores three solo
home runs, no individual home run is a but-for cause of the
outcome; had any single run not been scored, the team still
would have won. But each home run is a sufficient cause of
the result. See Burrage, 571 U.S. at 211–12, 214–15.6
Returning to the present context, imagine that the FDA has
long required ANDAs to satisfy two hypothetical
Requirements, 1 and 2. Each Requirement involves
conducting a distinct type of study, and failure to conduct either
one before the 30-month deadline would prevent approval. If
an applicant failed to satisfy both Requirements by the
deadline, each failure would be an independently sufficient
cause of the FDA’s consequent decision not to approve the
ANDA. But neither failure would constitute a but-for cause.
Failing to satisfy Requirement 2 is not a but-for cause because,
6
There can, of course, be multiple but-for causes of a single
event. See Dobbs et al., supra, § 186 (“It is by no means true that
the but-for test reduces everything to a single cause.”). Consider
another baseball game, this one ending 1-0 after the winning team hit
a one-run home run. That home run is a but-for cause of the victory,
as are “a host of other necessary causes, such as skillful pitching”
and even “the league’s decision to schedule the game.” Burrage,
571 U.S. at 212.
19
even “without” that failure, the same result (no approval)
would have occurred given the failure to satisfy Requirement
1—and vice versa. See Nassar, 570 U.S. at 347.
To bring the stakes of the parties’ dispute into focus,
imagine the same facts except that Requirement 2 was imposed
just before the 30-month deadline, such that it constitutes “a
change in . . . the requirements for approval” under 21 U.S.C.
§ 355(j)(5)(D)(i)(IV). Whether the first applicant can benefit
from the forfeiture exception turns critically on whether the
statute incorporates only strict but-for causation, or the
exception for independently sufficient causes too. Under a
strict but-for rule, the applicant’s failure to timely obtain
tentative approval was not “caused by” the FDA’s change.
Even if Requirement 2 was never imposed, the FDA would not
have granted approval based on the applicant’s failure to meet
Requirement 1. Under the multiple-sufficient-causes
exception, however, the applicant’s failure to obtain tentative
approval was “caused by” the change to Requirement 2. The
applicant would therefore avoid forfeiture despite its separate
failure to satisfy Requirement 1.
We hold that the phrase “caused by” in 21 U.S.C.
§ 355(j)(5)(D)(i)(IV) is best read to require a but-for analysis,
without the exception FDA urges here. Although the statute
does not define “caused by,” the “requirement of but-for
causation” is “part of the common understanding of cause” and
so is “one of the traditional background principles against
which Congress legislates.” Burrage, 571 U.S. at 211, 214
(cleaned up). Across myriad contexts, courts have held that
similar causal phrases such as “results from,” “because of,”
“based on,” and “by reason of” refer to but-for causation. Id.
at 210–14. And the general rule is that courts deviate from
that standard only where “textual or contextual indication[s]”
suggest that but-for causation is inappropriate. Id. at 212; see
20
Sinclair Wyo. Refin. Co. LLC v. EPA, 114 F.4th 693, 708–09
(D.C. Cir. 2024).7
As the Supreme Court has explained, the exception for
“multiple sufficient causes” is reserved for the “rare” instances
when adherence to strict but-for causation would produce
perverse results. Burrage, 571 U.S. at 214.
To illustrate, if “A stabs B, inflicting a fatal wound;
while at the same moment X, acting independently,
shoots B in the head . . . also inflicting [a
fatal] wound; and B dies from the combined effects of
the two wounds,” A will generally be liable for
homicide even though his conduct was not a but-for
cause of B’s death (since B would have died from X’s
actions in any event).
Id. at 215 (quoting 1 W. LaFave, Substantive Criminal Law
§ 6.4(a), at 468 (2d ed. 2003)). Applying strict but-for
causation in the situation of joint wrongdoers would have the
absurd effect of allowing both to escape liability. As the Court
put it in Paroline v. United States, 572 U.S. 434 (2014), courts
have sometimes “departed from the but-for standard where
circumstances warrant, especially where the combined conduct
of multiple wrongdoers produces a bad outcome.” Id. at 451;
7
We emphasize that we are presented with, and therefore reject,
only the multiple-sufficient-causes exception the FDA has urged
here. In a situation where the FDA changes multiple requirements,
it might be appropriate to adopt a “variation” of the but-for test
whereby multiple actions are “aggregated and considered as a
whole.” Dobbs et al., supra, § 189. In that situation, the but-for
test could be applied to the “unit or set” of changes, and “[i]f the
combined conduct is a but-for cause” of the resulting event, “then
cause is established.” Id. For example, in our hypothetical above,
if both Requirements 1 and 2 were imposed just before the deadline,
perhaps the combined “change” could be regarded as a but-for cause.
21
see also Dobbs et al., supra, § 189 (explaining that courts
recognize independently sufficient causes where a strict but-for
test would “violat[e] both an intuitive sense of causation and
good legal policy” by giving “a windfall to [] negligent
defendants”); Restatement (Third) of Torts: Liability for
Physical and Emotional Harm § 27 cmt. c (A.L.I. 2010) (June
2026 update) (“A defendant whose tortious act was fully
capable of causing the plaintiff’s harm should not escape
liability merely because of the fortuity of another sufficient
cause.”); Keeton et al., supra, 267 (similar).
The primary authority the FDA offers in support of
importing the multiple-sufficient-causes exception here fits
that same mold. In Kilburn v. Socialist People’s Libyan Arab
Jamahiriya, 376 F.3d 1123 (D.C. Cir. 2004), we interpreted a
jurisdictional provision of the Foreign Sovereign Immunities
Act. Under that provision, foreign sovereigns are not immune
from damages suits for “personal injury or death” “caused by”
violent acts such as “torture” and “extrajudicial killing.” Id. at
1126. The foreign defendants argued that this provision
required but-for causation. But that standard would have
meant that if two state sponsors of terrorism jointly caused
personal injury or death through a combination of
independently sufficient acts, courts would have jurisdiction
over neither of them. We rejected that argument, explaining
that applying “a ‘but-for’ standard to joint tortfeasors could
absolve them all,” which is “precisely” the situation in “which
courts generally regard ‘but for’ causation as inappropriate.”
Id. at 1129.
Here, however, there is no indication that departing from
but-for causation in Section 355(j)(5)(D)(i)(IV) would best
capture “congressional intent.” Paroline, 572 U.S. at 458.
Quite the opposite. The statutory baseline is that an
applicant’s failure to obtain tentative approval within 30
months warrants forfeiture. Applying a but-for causation
22
standard ensures that an applicant is excused from that failure
only if that applicant would have timely secured tentative
approval absent some relevant FDA “change in or . . . review
of the requirements.” 21 U.S.C. § 355(j)(5)(D)(i)(IV).
Applying the exception for independently sufficient causes, by
contrast, would “absolve” first applicants of their failure to
secure tentative approval even if their ANDA included one or
more critical deficiencies that would independently have
prevented approval. Kilburn, 376 F.3d at 1129.
Return to our Requirement-1-and-2 hypothetical above:
Suppose the first applicant simply could not, ever, meet
Requirement 1. So it knows that it is barreling towards a
forfeiture at the 30-month mark. But—through pure
serendipity—the FDA changes Requirement 2 just before the
30-month deadline, and the first applicant is unable to timely
comply with the revision. Under the FDA’s rule, that change
excuses the applicant’s failure to receive approval, and thereby
keeps subsequent applicants held up by the first applicant’s
exclusivity period, even though that applicant would not have
received approval anyway. There is no reason to think
Congress intended to grant deficient ANDAs that kind of
windfall.8
The FDA’s remaining arguments—its “longstanding”
practice and the difficulty of conducting but-for analysis,
FDA’s Brief 45—do not undercut this conclusion. We do not
defer to agency interpretations of statutes, particularly where,
as with “caused by,” the agency’s “technical subject matter
expertise” has “little to do with” the term in need of
8
Indeed, deviating from strict but-for causation could
conceivably undermine the statutory scheme in other ways. For
instance, the FDA might delay improving its requirements if it knew
that such changes might inadvertently preserve the exclusivity of a
fundamentally deficient ANDA that would otherwise soon forfeit it.
23
clarification. Loper Bright, 603 U.S. at 402. Moreover,
though we have no basis to doubt the FDA’s assertions that a
but-for rule will present additional complexities, we are
confident the agency’s experience with such applications will
enable it to devise an administrable framework for assessing
causation in a way consistent with the “best reading of the
statute.” Id. at 400.
2
Finally, we conclude that the FDA should conduct the but-
for-causation analysis in the first instance. Norwich urges us
to pursue and resolve that inquiry, but we decline to do so and
instead follow our customary practice of “remand[ing] to the
agency for additional investigation or explanation” in light of
the agency’s legal error. FDA v. Wages & White Lion Invs.,
LLC, 604 U.S. 542, 587 (2025) (quoting Fla. Power & Light
Co. v. Lorion, 470 U.S. 729, 744 (1985)).
According to Norwich, the outcome of a remand is
“preordained” because the administrative record conclusively
establishes that no change in or review of requirements caused
Actavis’s failure to obtain tentative approval, and the FDA has
forfeited any argument to the contrary. Appellant’s
Supplemental Brief 8. We disagree.
Once the FDA determined that its March 2017 draft
rifaximin-specific guidance was a cause of Actavis’s failure to
obtain tentative approval, it decided that it was “unnecessary to
determine whether any additional bases for non-forfeiture
exist[ed].” FDA’s Supplemental Brief 11–12 (quoting J.A.
363); see Norwich Pharms., 2025 WL 1148463, at *5. That
is, the FDA never considered whether some “change in or
review of” the requirements, other than the March 2017
guidance regarding “dissolution studies,” was a but-for cause
of Actavis’s failure to obtain tentative approval. For that same
reason, neither the FDA nor the intervenors forfeited the
24
argument that another change in or review of requirements
satisfies this exception merely because they failed to raise it
before the district court. Even if they had raised that
argument, the district court could not have affirmed on a basis
the agency itself did not articulate in the decision on review.
See SEC v. Chenery Corp., 318 U.S. 80, 95 (1943). Nor would
that court have been able to adequately evaluate such an
argument, had it been raised. To determine whether any other
change in or review of requirements was the but-for cause of
Actavis’s failure to obtain tentative approval, we would
properly consult the record for Actavis’s application. See
Salix’s Supplemental Brief 10; cf. FDA’s Supplemental Brief
1 n.1. Yet only the record for Norwich’s ANDA ’370 is
before us in this case.
Because there is “uncertainty as to the outcome of [the]
proceeding on remand,” we decline to resolve the but-for
causation analysis without giving the FDA the first
opportunity. Prohibition Juice Co. v. FDA, 45 F.4th 8, 24
(D.C. Cir. 2022) (quoting Manin v. NTSB, 627 F.3d 1239, 1243
n.1 (D.C. Cir. 2011)).
III
The district court’s grant of summary judgment is affirmed
in part and reversed in part. We affirm the court’s rejection of
Norwich’s “failure to market” theory of forfeiture. We
reverse its rejection of Norwich’s “failure to obtain tentative
approval” theory, and remand to the district court with
instructions to remand to the FDA so that the agency may apply
the but-for causation standard in the first instance.
So ordered.