A federal judge this week dealt a blow to more than 1,000 plaintiffs who say that using the popular erectile dysfunction drug Viagra caused them to develop melanoma—that is, skin cancer—or to accelerate the melanoma that they had already contracted. In his 24-page ruling handed down Monday in the Northern District of California, United States District Judge Richard Seeborg refused to allow testimony from medical and scientific experts who would link the drug to the potentially deadly cancer.
The ruling likely puts an end to the nationwide lawsuits, by preventing the plaintiffs from presenting medical evidence to support their contention that Viagra causes or worsens melanoma.
Seeborg said that no other evidence supported what the plaintiffs’ expert witnesses were expected to say, according to a report by Law.com. That is, that use of Viagra, also known by the generic name sildenafil, actually caused skin cancer, or exacerbated existing cancers.
“There simply is no interpretation by anyone other than plaintiffs’ experts that supports general causation,” Seeborg wrote. “On that critical question, despite substantial research on the issue over many years, plaintiffs’ experts apparently stand alone.”
His ruling comes after four days of testimony last October, in hearings aimed at determining which expert witnesses would be allowed to testify in the numerous lawsuits.
A scientific study published in 2014 found that Viagra users faced an 84 percent greater risk of developing the form of cancer that claims more than 8,600 lives each year in the United States alone. Melanoma is largely curable when detected early. But the disease becomes untreatable and generally fatal when the cancer spreads beyond the skin and into a patient’s lymph nodes.
The lawsuits claim that Pfizer, the pharmaceutical firm that manufactures Viagra, failed to warn users of the skin cancer risks allegedly associated with use of the ED drug. With a warning, the plaintiffs say, they could have avoided a melanoma diagnosis altogether, or prevented the deadly spread of the cancer cells.
The 2014 study, however, found only a correlation, not a causal link between Viagra use and melanoma. The study also found no link between use of the drug and the somewhat less deadly forms of skin cancer, squamous cell carcinoma and basal cell carcinoma.
The researchers speculated that use of the drug may cause a decrease in PDE5A, a protein produced by the human body which helps to prevent or contain the spread of cancer. Without sufficient levels of the protein, cancers can spread at more rapid rates.
“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,” Seeborg wrote in his ruling.
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