Viagra.

In a move likely to end the multidistrict litigation over Viagra, a federal judge struck all the plaintiffs' causation experts in cases alleging the erectile dysfunction medication increased the progression of melanoma.

In a Monday order, U.S. District Judge Richard Seeborg of the Northern District of California tossed out three experts, concluding that, unlike the experts evaluating similar studies about the herbicide Roundup, they did not present "a faithful application of an accepted methodology."

"While the studies here likewise may be subject to differing interpretations as to biological plausibility, or as to how strong the evidence is for an actual association, there simply is no interpretation by anyone other than plaintiffs' experts that supports general causation," he wrote. "On that critical question, despite substantial research on the issue over many years, plaintiffs' experts apparently stand alone."

Seeborg also refused to grant plaintiffs' motion to exclude six of the nine defense experts whose testimony focused primarily on refuting the plaintiffs' experts.

He ordered both sides to submit a joint statement in 20 days outlining "what steps should now follow in this litigation."

The Viagra ruling is a win for attorney Loren Brown, a New York partner and global co-chairman of the litigation practice at DLA Piper. Brown filed the motion to exclude all six plaintiffs' experts, including the three testifying on general causation, on behalf of Pfizer Inc., which makes Viagra. Also on the motion were Washington attorneys Joseph Petrosinelli, chairman of Williams & Connolly, for Pfizer, and Michael Imbroscio, co-chairman of the products liability and mass tort practice at Covington & Burling, who represented Eli Lilly & Co., which makes Cialis.

Brown and Imbroscio declined to comment, and Petrosinelli referred requests for comment to Pfizer. In a statement, Pfizer said the ruling portended the end of the Viagra litigation, which involves more than 1,000 lawsuits: "We have believed all along that, as the court has now ruled, there is no reliable scientific evidence that Viagra causes the injuries alleged in this litigation.  Absent admissible general causation testimony, we believe that all plaintiffs' cases will be required to be dismissed."

Lead plaintiffs attorneys Ernest Cory of Birmingham, Alabama's Cory Watson; Munir Meghjee of Robins Kaplan in Minneapolis; and Jennifer Liakos, a partner in the Los Angeles office of Napoli Shkolnik, did not respond to a request for comment.

Plaintiffs lawyers filed the lawsuits soon after a 2014 study published in a journal of the American Medical Association that found a "significantly elevated risk of invasive melanoma" in patients who used sildenafil, sold under the brand name Viagra. Several studies followed, but both sides in the lawsuits disagreed on the significance of their findings.

In October, Seeborg held four days of hearings to determine which experts to allow in the cases, under the U.S. Supreme Court's 1993 decision in Daubert v. Merrell Dow Pharmaceuticals.

In his order, Seeborg disagreed with the defendants on three plaintiffs' experts who concluded it was "biologically plausible" that Viagra increased the progression of melanoma, the deadliest form of skin cancer. He wrote that those experts had "reliably applied accepted scientific methods in reaching their conclusions."

He agreed with the defendants, though, as to the plaintiffs' general causation experts. Those three experts were: Rehana Ahmed-Saucedo, assistant professor of dermatology at the University of Minnesota Medical School; Sonal Singh, associate professor at the University of Massachusetts Medical School; and Feng Liu-Smith, assistant professor at the University of California Irvine School of Medicine. Seeborg concluded that those experts relied on the consistent findings of the epidemiological studies, which showed an increased risk—but only around 1.2%.

"Although a risk factor in that range would not necessarily preclude a conclusion that causation exists, it undeniably is not a strong association," he wrote.

In their opposition to exclude their experts, plaintiffs attorneys cited a 2018 ruling in another cancer case by Seeborg's colleague, U.S. District Judge Vince Chhabria of the Northern District of California, who refused to toss plaintiffs' experts in cases over the herbicide Roundup despite "a very close question" about their admissibility. According to the Viagra plaintiffs attorneys, the experts in Roundup had relied on studies with "exceptionally weaker showing in consistency and statistical significance," but that "these weaknesses did not induce the court to exclude the epidemiological experts' testimony."

In his order, Seeborg distinguished the Viagra studies from those in Roundup.

"Plaintiffs have been unable to point to any conclusion reached by any scientist, researcher, regulatory agency, or other qualified person or group apart from their experts in this litigation that use of PDE5 inhibitors causes melanoma progression," he wrote. "That fact alone puts this case in stark contrast to Roundup, where the International Agency for Research on Cancer, which is the specialized cancer agency of the World Health Organization, had classified the substance at issue as 'probably carcinogenic to humans.'"

The inclusion of the IARC finding meant that in Roundup, unlike Viagra, the experts reached conclusions that were "outside the context of litigation," he wrote.

Last year, a federal jury in the first bellwether trial in the Roundup multidistrict litigation awarded $80 million to a couple claiming they got non-Hodgkin lymphoma from exposure to the herbicide, sold by Monsanto Co., now owned by Bayer AG. Monsanto, which also lost verdicts of $2 billion and $289 million in California state courts, has challenged the scientific evidence in a petition before the U.S. Court of Appeals for the Ninth Circuit.