First Circuit Adopts Defense-Friendly “But-For” Causation Standard for AKS-Predicated FCA Claims

In a unanimous panel opinion filed on February 18, 2025, the First Circuit held that False Claims Act cases predicated on violations of the Anti-Kickback Statute (“AKS”),¹ require proof that alleged kickbacks were the “but-for” cause of the challenged claims.² Put another way, the government bears the burden “of proving that an AKS violation actually caused a physician to provide different medical treatment (and thus caused the false claims).”³

Under a 2010 amendment to the statute (42 U.S.C. § 1320a-7b(g)), “claim[s] that include items or services resulting from a violation of this section constitute false or fraudulent claim[s]” under the False Claims Act (“FCA”).⁴  But whether “resulting from” requires but-for causation or a more lenient causation standard has been a question percolating among the circuit courts in recent years.

The First Circuit joins the Sixth and Eighth Circuits, which have also held that “resulting from” requires but-for causation.⁵ In contrast, the Third Circuit held in 2018 that the statutory language does not require but-for causation but instead merely requires some connection between the kickbacks and the challenged claims.⁶ The First Circuit’s decision thus represents a growing, lopsided circuit split, setting up an eventual Supreme Court challenge on the issue. The First Circuit’s decision also provides further legal support for companies defending AKS-predicated FCA claims.

Background

The United States brought this case against Regeneron Pharmaceuticals, Inc., alleging that Regeneron “improperly funneled millions of dollars to the Chronic Disease Fund,” (“CDF”) which was a “purportedly charitable foundation” in order “to subsidize patient copays for Eylea” to increase prescriptions for the drug.⁷ Regeneron moved for summary judgment, arguing in part that the government could not prove that Regeneron’s donations resulted in the submission of false Medicare claims.⁸  The district court held that the “resulting from” language in the AKS requires a but-for causation standard.  However, the court held that the issue of AKS causation could withstand summary judgment given the government had submitted a report from an expert who had analyzed CDF disbursement data and performed a “matching” analysis to identify Medicare claims for which CDF paid all or some of the copay.⁹ And in addition to its expert report, the government also pointed to evidence that physicians may have prescribed a lower-priced drug in the absence of the co-pay subsidies.¹⁰

The district court subsequently certified this portion of its decision for interlocutory appeal so that the First Circuit could assess the but-for causation issue.¹¹

The First Circuit, in its recent decision, agreed with the district court that a but-for causation standard applies to AKS-predicated FCA claims.  The First Circuit noted that phrases like “resulting from” impose “actual causality” requirements, which, in the usual course, follow a but-for standard.¹²  While noting that courts may deviate from a but-for standard where there are “textual or contextual indications” for doing so, the court did not find any such indications that would support deviating from a but-for standard.¹³

The First Circuit also explained that 42 U.S.C. § 1320a-7b(g) is not the exclusive path to establishing FCA liability based on AKS violations.  The government, or a relator, can also allege that a defendant has falsely certified compliance with the AKS and therefore submitted false and fraudulent claims.  This would require proof that such certification was material to payment but would not require evidence of a but-for causation link between the alleged AKS violation and the claims.

Implications

The First Circuit’s decision solidifies a 3-1 circuit split on the issue, with the Third Circuit standing alone in holding that but-for causation is not required under the “resulting from” language, but instead an FCA plaintiff must show some “link” between the AKS violation and the challenged claims.¹⁴ This growing circuit split provides companies with a potential basis to challenge AKS-predicated FCA claims, particularly where there is weak evidence of a causal connection between alleged kickbacks and challenged claims.

The circuit split may also eventually make its way up to the Supreme Court, which could provide clarity and consistency on the issue were it inclined to take it up.

^[1] 42 U.S.C. § 1320a-7b(b).
^[2] United States v. Regeneron Pharms., Inc., No. 23-2086, 2025 WL 520466 (1st Cir. Feb. 18, 2025).
^[3] Id. at *2 (cleaned up and emphasis added).
^[4] 31 U.S.C. §§ 3729-33
^[5] United States ex rel. Martin v. Hathaway, 63 F.4th 1043, 1052–55 (6th Cir. 2023); United States ex rel. Cairns v. D.S. Med. LLC, 42 F.4th 828, 834–35 (8th Cir. 2022).
^[6] Greenfield v. Medco Health Sols., Inc., 880 F.3d 89, 100 (3d Cir. 2018).
^[7] United States v. Regeneron Pharms., Inc., No. CV 20-11217-FDS, 2023 WL 6296393, at *1 (D. Mass. Sept. 27, 2023).
^[8] Id. at *3.
^[9] Id. at *12
^[10] Id.
^[11] United States v. Regeneron Pharms., Inc., No. CV 20-11217-FDS, 2023 WL 7016900, at *1 (D. Mass. Oct. 25, 2023).
^[12] Regeneron Pharms., Inc., 2025 WL 520466, at *3.
^[13] See id., at *5-10. 
^[14] Greenfield, 880 F.3d 98

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