In a significant win for pharmaceutical and other defendants in Texas product liability cases, the Texas Supreme Court on Friday, August 26, 2011 issued its opinion in Merck & Co. v. Garza, reaffirming its landmark decision in Merrill Dow Pharmaceuticals, Inc. v. Havner, in which the court set forth requirements for determining whether epidemiological evidence is sufficiently scientifically reliable to prove causation. The Garza opinion provides welcome clarification that Havner establishes bright-line, minimum criteria for reliability that apply to observational epidemiological studies and clinical trials alike.

The case arose from the April 2001 death of Leonel Garza, a 71-year-old heart patient who suffered a fatal heart attack while allegedly taking a 30-day prescription of Vioxx for left arm pain. Mr. Garza’s family sued Merck in Starr County, Texas, and secured a $7.75 million judgment. The San Antonio Court of Appeals rejected Merck’s arguments concerning the scientific reliability of the Garzas’ expert opinion evidence that Mr. Garza’s short-term Vioxx use was a producing cause of his death but remanded the case for a new trial based on jury misconduct.

Merck petitioned the Texas Supreme Court for review, asking the court to clarify certain issues arising under Havner. Specifically, Merck asked the court to hold that its Havner causation requirements—that, as a matter of law, causation cannot be established with epidemiological studies unless the plaintiff presents evidence of at least two statistically significant studies showing a greater-than-doubling of the risk at the same or lesser dose and duration as the plaintiff’s—constitute minimum requirements that must be satisfied in every case. Merck also asked the court to hold that the Havner requirements apply not only to observational epidemiological studies, like those at issue in Havner, but also to clinical trials, which generally are more reliable.

The Texas Supreme Court agreed with Merck, reversing the court of appeals’ judgment and rendering judgment in Merck’s favor. The court held expressly, for the first time, that Havner’s requirements apply to all epidemiological evidence, including clinical trials. The court recognized that the controlled, experimental, and prospective nature of clinical trials makes them more reliable than retroactive, observational studies but concluded that clinical trials still are only capable of providing indirect proof of causation. Accordingly, clinical trials must satisfy Havner’s requirements for such indirect proof.

The court also confirmed that Havner’s requirements for epidemiological evidence are bright-line, minimum criteria. A plaintiff relying on epidemiological evidence as proof of general causation must come forward with at least two studies showing a statistically significant doubling of the risk at essentially same dose and duration as the plaintiff. Only if the studies meet these threshold requirements of reliability may a court go on to conduct the secondary reliability inquiry that examines the soundness of the study’s findings using the totality of the evidence test. The law is now clear that two statistically significant studies showing a doubling of the risk are necessary but may not be sufficient if the totality of the evidence indicates that reliable conclusions about causation cannot be drawn from the studies.