A new study suggests the higher rate of melanoma found among Viagra users may be related to Viagra users’ lifestyles.

The study, published in the Journal of the American Medical Association, looked at the medical records of over 20,000 men registered with the National Melanoma Register and the Prescribed Drug Register in Sweden. The research focused on men who took erectile dysfunction drugs known as phosphodiesterase type 5 inhibitors (PDE5 inhibitors), a class of drugs that includes Viagra (silldenafil), Levitra (vardenafil), and Cialis (tadalafil). Researchers compared the rates of skin cancer in men who took these drugs with the rates in men who didn’t an increased risk of melanoma skin cancer.

The researchers found a “modest but statistically significant” increase in the risk of malignant melanoma in men who took PDE5 inhibitors. They noted the most pronounced increase occurred in men who filled only a single prescription, while men who filled multiple prescriptions did not show a significant increase. That finding raised a question as to whether an association between PDE5 inhibitors and melanoma could be causal. If there were a causal connection between Viagra and melanoma, the researchers state they would have expected to find the opposite results: a higher rate of melanoma occurring with more use of the drug.

Researchers also noted that men who take PDE5 inhibitors tend to have more education and higher income, both of which are significantly associated with melanoma risk. Indeed, at up to $50 per pill, Viagra isn’t cheap, and insurance doesn’t cover it. As a result, men who take Viagra are more likely to be able to afford lots of sunny outdoor leisure time, which comes with a higher risk of skin cancer.

Earlier Evidence of Viagra Melanoma

The new Viagra melanoma study sheds more light on an older study published in JAMA Internal Medicine in 2014, which raised the possibility of a link between Viagra and melanoma.

The earlier study was spurred by research showing that Viagra mimics parts of the process by which melanoma cells spread to other parts of the body. The researchers in the 2014 study analyzed information collected in Harvard University’s Health Professionals’ Follow-up Study, a long-term project used to collect information about individual men’s health and lifestyles.

The researchers looked at information gathered from over 25,000 men over a ten-year period, in order to compare the experiences of men who took Viagra to those who didn’t. They found that 8.6 men out of every 1,000 who took Viagra developed skin cancer, which for purposes of this study included melanoma, squamous cell carcinoma, and basal cell carcinoma. Among men who did not use Viagra, skin cancer occurred in only 4.3 out of every 1,000 men.

With statistical adjustments, the rate of incidence of skin cancer was 84 percent higher for Viagra users, a rate the researchers determined was statistically significant. The rate was higher both with men who had taken Viagra recently and with those who had taken it at any time in their lives. The researchers concluded that Viagra (or more specifically sildenafil, the active ingredient in Viagra) could be associated with an increased risk of melanoma.

The researchers did not find sufficient evidence to establish a causal relationship between Viagra and melanoma. However, they did conclude that the possibility of a relationship between the two called for further investigation.

So what should men taking Viagra do to avoid skin cancer? Experts say there’s not enough information to support a recommendation against taking Viagra. They say it’s better to simply avoid sun exposure and keep an eye out for new skin growths that might lead to melanoma.