In a recent lawsuit deposition, a prominent oncologist claimed that the side effects of Viagra and similar drugs include an increased risk of skin cancer.

Dr. Rizwan Haq, an assistant professor at the Farber Cancer Institute, said, “There is a biologically plausible mechanism” in Viagra that can accelerate the progression of melanoma. He says his opinion is based on an analysis of approximately 50 studies.

About Viagra

Available in generic form as sildenafil, Viagra was first developed by Pfizer in the mid-1990s. Originally, the company was attempting to develop a treatment for hypertension and angina pectoris (chest pain caused by coronary heart disease). During clinical trials, it proved ineffective for angina, but it was discovered that it could induce “marked penile erections” in male subjects.

It was then decided to market the drug for sexual dysfunction in men, an indication for which the FDA granted approval in March 1998. Within a decade, Viagra sales came to almost $2 billion a year.

In addition to erectile dysfunction (ED), Viagra may also be prescribed for pulmonary arterial hypertension. Other medications in this class include Cialis (tadalafil) and Levitra (vardenafil). Some medical researchers believe these drugs may also cause an elevated risk of melanoma.

The Evidence

Dr. Haq reportedly provided his testimony on the side effects of Viagra to U.S. District Judge Richard Seeborg, who is currently determining if the scientific evidence is sufficient to warrant taking current claims against the drug makers to trial.

In addition to Pfizer, Cialis-maker Eli Lily has also been named as a defendant. Viagra and other medications of its class are known as phosphodiesterase type 5 (PDE5) inhibitors. PDE5 is an enzyme that occurs naturally in the tissues of the penis and the retina. Normally, PDE5 breaks down a substance called cyclic guanosine monophosphate cGMP, a biochemical that relaxes smooth muscle tissues around the blood vessels. Viagra prevents PDE5 from acting on cGMP, thus increasing blood flow.

According to Dr. Haq, PDE5 is also found in melanoma cells. He believes that melanoma uses the same biological pathways as Viagra.

The Defense Responds

Counsel for Pfizer responded to Dr. Haq’s allegations by pointing out that he is one of only three research scientists who have stated they have found a link between the side effects of Viagra and melanoma. The defense also points out that no other physicians, researchers, regulators or medical associations – including the American College of Dermatology – have come to this conclusion. Pfizer believes that men who take Viagra or Cialis simply get more sun exposure.

Other Side Effects of Viagra

In addition to the possible link to skin cancer, common adverse effects of Viagra include:

• flushing
• headaches
• impaired vision
• indigestion
• nasal congestion

Several studies have also found a link between Viagra and damage to the optic nerve due to insufficient blood flow.

Less frequently, Viagra can cause prolonged, painful erections, serious hypotension, heart attack, irregular heartbeat, stroke and hearing loss. A warning about hearing loss has been required on the package labeling since 2007.