Insights & Events

The United States Court of Appeals for the Ninth Circuit recently affirmed a district court’s grant of summary judgment to defendant Eli Lilly & Co. based on plaintiff’s failure to establish proximate causation under the learned intermediary doctrine (“LID”). Dearinger v. Eli Lilly & Co., No. 24-682, 2026 WL 788866 (9th Cir. Mar. 20, 2026). This case addresses novel challenges to the LID that plaintiffs may raise again in the future given the realities of modern medicine.

In Dearinger, the plaintiff alleged that, in 2018, he experienced an intracranial brain hemorrhage, i.e., a stroke, as a result of taking Eli Lilly’s FDA-approved prescription erectile dysfunction drug Cialis. Beginning in 2007, the plaintiff’s urologist had prescribed a 20 mg dose of Cialis to take on an as-needed basis. In 2015, the urologist modified the prescription to a daily 5 mg dose. By March 2017, plaintiff was no longer seeing the urologist and instead received a refill of the daily 5 mg dose from his primary care physician (“PCP”). The plaintiff testified that on the day he experienced a stroke in 2018, he had taken one of the 20 mg Cialis pills prescribed by the urologist in 2007 instead of one of the 5 mg pills from the PCP’s current prescription. At deposition, the urologist unambiguously testified that he understood that strokes had been reported in patients taking Cialis and that a stronger warning—including the one that plaintiff proposed would be adequate—would not have changed his decision to prescribe Cialis to plaintiff. Eli Lilly moved for summary judgment, arguing that the urologist’s testimony was dispositive on the issue of proximate cause. The district court agreed and granted summary judgment.

On appeal, plaintiff argued that the lower court erred by focusing on the urologist’s testimony instead of the PCP’s deposition testimony. The PCP testified that had he been given plaintiff’s proposed warning, he would not have prescribed Cialis to someone with plaintiff’s “family history” and would have “hesitated” to prescribe Cialis to plaintiff. Plaintiff argued that proximate cause could be satisfied by the PCP’s testimony, either as an additional prescriber or as a treating physician who could have told plaintiff to discontinue using Cialis prescribed by someone else. The Ninth Circuit found that, because the PCP did not prescribe the 20 mg Cialis pill that plaintiff took on the morning of his alleged injury, his testimony that he would not have prescribed plaintiff Cialis if he was given a different warning could not establish proximate causation between the alleged lack of adequate warnings and the alleged injury. The Circuit Court also held that the PCP’s testimony could not cure the broken causal chain because a drug manufacturer’s duty to warn does not extend to a patient’s non-prescribing treating physicians. See Dearinger, 2026 WL 788866, at *2.

In modern medical practice, it is not uncommon for individuals to receive care from multiple physicians for the same conditions. Plaintiffs may argue that this can complicate the application of the LID, which holds that a drug or medical device manufacturer satisfies its duty to warn by providing adequate warnings to, specifically, the patient’s prescribing physician, not to the patient. Under the LID, testimony of the prescribing physician can be dispositive of a plaintiff’s failure to warn claims—for example, testimony that the physician would have prescribed the drug or device, even if a proposed alternative warning had been provided, breaks the chain of proximate causation. See Aleksandra Rybicki and Olivia N. Sacks, Using the Learned Intermediary Doctrine at Each Stage of the Litigation, DRI For the Defense, October 2025 at 7. Under the Ninth Circuit’s holding, a manufacturer’s duty to warn runs solely to the physician who prescribed the specific drug that led to the plaintiff’s alleged injury. It follows that a plaintiff cannot prove proximate cause with the testimony of a non-prescribing physician, where the prescribing physician has testified that a different warning would not have changed his prescribing decision.

The Ninth Circuit’s decision in Dearinger is the right result as a matter of policy: the prescribing physician of the medication alleged to have caused the injury at issue is best situated, in light of his education, training, experience, and relationship with the patient, to weigh the benefits and risks of treatment for an individual patient’s particular medical condition, and to relay relevant information to the patient. When prescriber testimony establishes that the alleged lack of a warning made no difference in their prescribing decision, the testimony of a non-prescribing physician cannot overcome that dispositive testimony and cure the break in the causal chain.

— By Aleksandra Rybicki and Olivia Sacks