SAN FRANCISCO (CBS SF) — Over 200 men who took Viagra say the drug increased their risk of developing melanoma. Now they’re suing pharmaceutical giant Pfizer Inc., claiming negligence and failure to warn them of the erectile dysfunction drug’s danger.

Lawsuits against Pfizer are being filed almost daily, all claiming almost the exact same thing: that they developed melanoma after taking Viagra.

But Pfizer maintains that there is no scientific evidence supporting a cause and effect relationship between the use of Viagra and the development of the deadly skin cancer, melanoma, which has long been linked to increased exposure to ultraviolet radiation.

The flood of lawsuits began after the publication of a 2014 study in the Journal of American Medical Association.

The study’s authors state that while they did not find that using Viagra, which also goes by its generic name sildenafil citrate, caused melanoma to develop, they found that “Sildenafil use may be associated with an increased risk of developing melanoma.”

Dr. Wen-Qing Li, now a professor of dermatology and epidemiology at Brown University, is one of the main authors of the 2014 study.

When the study was published, Li was a research fellow at Harvard Medical School’s Brigham and Women’s Hospital.

Li told CBS San Francisco more about the study that has now prompted hundreds of lawsuits to be filed by people around the country.

Li said he and his fellow researchers “have done comprehensive analysis examining the associations between Viagra use and risk of melanoma and found a positive association.”

The results, Li explained, are based on a well-established and long-term cohort study. And while the results suggest a robust and positive association between sildenafil use for erectile dysfunction and risk of subsequent melanoma, Li insists that the “results should be interpreted cautiously and are insufficient to alter current clinical recommendations.”

Li said there is a need for continued investigation of the relationship between Viagra and melanoma.

By April, however, there were so many lawsuits filed that the cases were consolidated in the Northern District of California.

Since Viagra was approved by the FDA in 1998, the drug has been prescribed to more than 68 million patients worldwide.

In 2015, Viagra generated $1.7 billion in revenue for Pfizer.

Viagra is a type of drug known as a PDE5 inhibitor. This inhibitor, according to previous studies published in 2011 and 2012, may increase the invasiveness of melanoma cells.

Sildenafil citrate (FDA)

Sildenafil citrate (FDA

While some of the 200 plaintiffs are now living with melanoma, others are suing on behalf of someone who died of melanoma after taking the little blue pill.

The plaintiffs maintain that they had a right to know about the inhibitor’s positive association with melanoma and argue that if they had known, they would not have taken the drug.

The plaintiffs allege that Pfizer as well as other manufacturers of PDE5 inhibitors failed to warn consumers and health care providers. Other PDE5 inhibitors approved by the FDA are tadalafil, known as Cialis, and vardenafil, known as Levitra.

The latest complaint, filed on Friday on behalf of a man in North Carolina, states that the plaintiff took Viagra for 12 years spanning 2003 to 2015 and was first diagnosed with melanoma in 2009 and then again in 2013.

Some law firms have bought online advertisements in an effort to find additional plaintiffs who were diagnosed with melanoma after taking the drug.

Today, Viagra is still being prescribed and does not include warnings about the association between its use and melanoma.

A spokesperson for Pfizer Inc. said in a statement to CBS San Francisco regarding the lawsuits that, “Viagra’s safety and efficacy have been studied in 136 clinical trials, and there is no reliable scientific evidence that the medicine causes melanoma. Moreover, Viagra has been prescribed to millions of men worldwide since it was first approved by regulators 18 years ago, and this real world experience supports its favorable benefit-risk profile. Pfizer stands behind this medicine and will vigorously defend these lawsuits.”

A Northern District of California judge will ultimately decide whether there is sufficient causation between Viagra and melanoma to move the lawsuits forward.

By Hannah Albarazi – Follow her on Twitter: @hannahalbarazi.

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