Post-Ruan § 841 Instructions in the Fifth Circuit: No Separate “Good Faith” Charge Required When Mens Rea Is Tied to Unauthorized Prescribing

I. Introduction

In United States v. Mendez (5th Cir. Jan. 28, 2026) (per curiam) (unpublished), the Fifth Circuit affirmed the conviction and 84-month sentence of Dr. Leovares Mendez, a DEA-registered physician who operated a clinic in Garland, Texas. The Government alleged that Mendez and his business partner, Dr. Cesar Pena, unlawfully dispensed controlled substances to drug-seeking “patients,” including undercover DEA officers, by issuing prescriptions without a legitimate medical purpose and outside the usual course of professional practice.

The appeal raised three recurring issues in federal controlled-substance prosecutions of medical professionals: (1) what jury instructions satisfy Ruan v. United States for 21 U.S.C. § 841 prosecutions of prescribers; (2) what evidence suffices to prove a prescription-distribution conspiracy without an explicit agreement; and (3) what happens when a district court applies the U.S.S.G. § 3C1.1 obstruction enhancement without making detailed predicate perjury findings and the defendant raises the complaint for the first time on appeal.

II. Summary of the Opinion

The Fifth Circuit affirmed across the board. It held that the district court’s instruction—requiring the jury to find that Mendez “dispensed the controlled substance by a prescription knowingly or intentionally not used for a legitimate medical purpose in the usual course of professional practice”—adequately conveyed the required subjective mens rea under 21 U.S.C. § 841 as construed by Ruan v. United States. The court rejected Mendez’s claim that a separate “good faith” instruction was necessary.

On sufficiency, the court found ample evidence for conspiracy even absent an explicit agreement, emphasizing that a tacit agreement suffices. Finally, applying plain-error review, the court held that even if the district court erred by not expressly making predicate perjury findings to support the obstruction enhancement, Mendez failed to show any effect on his substantial rights.

III. Analysis

A. Precedents Cited

  • United States v. Ferris, 52 F.4th 235 (5th Cir. 2022): The panel used Ferris to frame the standards of review for jury-instruction challenges—abuse of discretion generally, but de novo (subject to harmless error) when an instruction is alleged to misstate an element of the offense. This matters because post-Ruan disputes often turn on whether the instructions correctly state the “authorization” element’s mens rea.
  • Ruan v. United States. 597 U.S. 450 (2022): The core substantive authority. The panel treated Ruan as requiring subjective mens rea for § 841’s “except as authorized” clause, rejecting convictions based on purely objective “reasonable doctor” measures when the defendant lacks the required knowledge or intent.
  • United States v. Capistrano, 74 F.4th 756 (5th Cir. 2023): The central Fifth Circuit gloss on Ruan. The panel relied on Capistrano both to (i) characterize Ruan as eliminating the Government’s ability to convict “without knowledge” based merely on objective deviation, and (ii) hold that a standalone “good faith” instruction is not required if the charge already ties “knowingly or intentionally” to the unauthorized nature of the prescribing.
  • United States v. Franklin, 838 F.3d 564 (5th Cir. 2016): Cited for invited-error principles. Because Mendez requested the specific relocation of “knowingly or intentionally” in the instruction, he could not later complain about the resulting “knowingly and intentionally” phrasing as error.
  • United States v. Lamartiniere, 100 F.4th 625 (5th Cir. 2024): Reinforced the post-Ruan proposition that linking “knowingly or intentionally” to “outside the usual course”/“no legitimate medical purpose” satisfies the subjective mens rea requirement without a special “good faith” instruction.
  • United States v. Harris, 740 F.3d 956 (5th Cir. 2014) and United States v. Moreno-Gonzales, 662 F.3d 369 (5th Cir. 2011): These cases supplied the sufficiency standard—de novo review, but highly deferential to the verdict—supporting the panel’s unwillingness to reweigh evidence about agreement and participation.
  • United States v. Westbrook, 119 F.3d 1176 (5th Cir. 1997): The key conspiracy doctrine: “[t]o be a conspiracy, an express, explicit agreement is not required; a tacit agreement is enough.” This precedent did the heavy lifting for affirming the conspiracy count in a clinic setting where coordination can be inferred from operational patterns rather than explicit statements.
  • United States v. Mondragon-Santiago, 564 F.3d 357 (5th Cir. 2009): Controlled the plain-error framework for unpreserved sentencing objections, particularly the requirement that the defendant show an effect on substantial rights. The panel used it to conclude that any failure to articulate perjury findings did not warrant relief absent a showing the sentence would have changed.

B. Legal Reasoning

1. Jury Instructions After Ruan: Mens Rea Must Attach to Unauthorized Prescribing, but “Good Faith” Need Not Be Separate

The panel’s instruction analysis proceeds in two steps. First, it acknowledges the post-Ruan baseline: § 841 prosecutions of registered prescribers require proof of a subjective culpable mental state as to acting “except as authorized.” That means the jury must be directed to decide whether the defendant knowingly or intentionally prescribed in an unauthorized way, not merely whether the prescriptions were objectively outside professional norms.

Second, the panel evaluates whether the instruction given accomplished that. The district court initially proposed language placing “knowingly or intentionally” earlier in the sentence, which could be read as attaching only to the act of dispensing. Mendez requested a modification to “more clearly link the mens rea requirement” to the illegitimate-purpose determination. The court adopted that edit. With the mens rea phrase now directly modifying “not used for a legitimate medical purpose in the usual course of professional practice,” the panel—relying on Capistrano and Lamartiniere—held the instruction sufficient.

The key doctrinal move is the court’s rejection of the argument that an additional “good faith” instruction was required. Although Mendez argued other parts of the jury charge referenced objective standards for “usual course” in the United States and might have confused jurors, the panel treated “knowingly or intentionally” tied to illegitimacy/outside-the-course as enough to ensure subjectivity in the ultimate question: did the defendant know (or intend) that he was prescribing without authorization.

2. Invited Error as a Backstop

The panel also invoked invited error (United States v. Franklin) to the extent Mendez complained about the final phrasing (“knowingly and intentionally”). Where a defendant requests a specific formulation and the court adopts it, appellate review is sharply constrained. In practical terms, the holding discourages defendants from strategically proposing language at trial and later attacking that same language on appeal.

3. Conspiracy Proof: A Tacit Agreement Can Be Inferred from Clinic Operations

On conspiracy, the panel applied the deferential sufficiency standard (United States v. Harris; United States v. Moreno-Gonzales) and the substantive rule that a conspiracy does not require an explicit agreement (United States v. Westbrook). The opinion highlights circumstantial evidence from which a jury could infer a shared unlawful plan:

  • Patterned “superbills” for drug-seeking patients (no services listed, “level 5” circled, $250 charged) contrasted with detailed documentation for legitimate patients.
  • Cross-coverage of each other’s drug-seeking patients, including issuing the same controlled substances and collecting the same $250 when the other doctor was unavailable.
  • Testimony that “it was nonetheless ‘understood’ what they were doing,” along with staff awareness of the drug-seeking clientele.
  • Undercover DEA visits over multiple years in which Mendez repeatedly prescribed controlled substances without meaningful examination or substantive inquiry.

The court’s reasoning underscores that, in controlled-substance clinic cases, “agreement” is frequently proved through standardized workflows, shared financial arrangements, consistent prescribing patterns, and mutual accommodation—rather than direct evidence like emails or recorded conversations.

4. Sentencing: Unpreserved Objection to Perjury Findings Fails Without a Showing of Prejudice

The district court applied U.S.S.G. § 3C1.1 after the Government argued Mendez committed perjury on material issues three times. The court sustained the objection “without further comment.” On appeal, Mendez argued the district court failed to make the necessary predicate finding of perjury.

Because Mendez did not request explicit findings at sentencing, the panel applied plain-error review (United States v. Mondragon-Santiago). Critically, the panel did not need to definitively decide whether the absence of explicit perjury findings was error; it held that even assuming error, Mendez failed to demonstrate the required prejudice—i.e., that a fuller explanation would have changed the sentence. Under the panel’s application of Mondragon-Santiago, a procedural sentencing complaint raised for the first time on appeal is unlikely to succeed absent a concrete, record-based argument that the guideline range or ultimate sentence would have been different.

C. Impact

Although designated “not for publication,” United States v. Mendez reflects (and reinforces) the Fifth Circuit’s operational approach to post-Ruan prescribing prosecutions:

  • Jury-instruction drafting: Trial courts can satisfy Ruan without a separate “good faith” instruction if they clearly connect “knowingly or intentionally” to the lack of legitimate medical purpose/outside-the-usual-course determination, consistent with Capistrano and Lamartiniere.
  • Defense strategy: Defendants should preserve instruction objections with specificity and caution when proposing alternative language; invited error can foreclose appellate relief.
  • Conspiracy theory viability: Prosecutors may continue to rely on tacit-agreement theories in “pill mill” or suspect clinic cases, building agreement through shared practices and financial/operational coordination rather than explicit communications.
  • Sentencing preservation: If a defendant believes the court must make explicit perjury findings for § 3C1.1, the objection must be raised at sentencing; otherwise, on appeal the defendant must show not just error, but a plausible change in the sentence.

IV. Complex Concepts Simplified

  • “Except as authorized” (21 U.S.C. § 841): Doctors can prescribe controlled substances only when the prescription is legally authorized—generally meaning it is issued for a legitimate medical purpose in the usual course of professional practice.
  • Subjective mens rea (after Ruan): The Government must prove what the prescriber actually knew or intended about the unauthorized nature of the prescribing, not just that the prescribing was objectively inconsistent with medical standards.
  • “Good faith” instruction: A jury instruction expressly stating that the defendant must be acquitted if he acted in good faith. The Fifth Circuit’s post-Ruan approach, as applied here, is that such an instruction is not required if the given instructions already require the jury to find the defendant acted knowingly or intentionally without legitimate purpose/outside professional practice.
  • Tacit agreement (conspiracy): A conspiracy can be proved by coordinated conduct and circumstances showing a shared plan, even without a written or spoken “deal.”
  • U.S.S.G. § 3C1.1 obstruction enhancement (perjury): A sentencing increase applied when a defendant obstructs justice, including by committing perjury. If the defendant does not preserve an objection to the court’s factual findings at sentencing, appellate review is limited and typically requires a showing that the outcome likely would have been different.
  • Plain error / substantial rights: A tough appellate standard applied to unpreserved claims. Even if there was a clear error, the defendant must show it likely affected the outcome.

V. Conclusion

United States v. Mendez consolidates several practical rules for Fifth Circuit criminal litigation in controlled-substance prescribing cases: (1) post-Ruan, instructions satisfy § 841’s subjective mens rea when “knowingly or intentionally” is clearly tied to unauthorized prescribing, and a separate “good faith” instruction is not mandatory; (2) conspiracy convictions can rest on tacit agreement inferred from clinic operations and shared practices; and (3) sentencing challenges to an obstruction enhancement raised for the first time on appeal will fail absent a concrete showing of prejudice. Even as an unpublished opinion, the decision is a clear signal of how the Fifth Circuit continues to implement Ruan through its own precedents, particularly United States v. Capistrano and United States v. Lamartiniere.