A shocking new study indicates that the millions of men who take Viagra and similar drugs to treat their erectile dysfunction may be at a greater risk of getting skin cancer, new research claims.

The study, conducted by New York University, involved 4,000 men in Sweden, and it found that those who took ED drugs were about a third more likely to develop malignant melanoma if prescribed just one course. For those with multiple courses prescribed, it was an increase of about 20 percent, according to a Telegraph report.

It’s still a pretty small risk, going up from 3 percent to 4 percent, but it’s a significant enough increase that it caught the attention of the researchers.

Erectile dysfunction drugs like Viagra and Cialis frees up the blood supply necessary for sex by turning off the enzyme PDE5. What does this have to do with melanoma? Scientists think that it comes about by a faulty gene suppressing this enzyme, which means that shutting off PDE5 may have the unintended side effect of increasing the risk that melanoma could develop. In fact, Viagra and similar drugs may actually be imitating the actions of this mutated BRAF gene.

Viagra created a marketing sensation when it was released in the 1990s, and has become an exceedingly popular pill among men who suffer from ED.

Some have downplayed these findings, arguing that it isn’t conclusive and there could be other factors at play that resulted in the increased risk of melanoma. One expert quoted in the report noted that there was correlation in the study between malignant melanoma and increased income, suggesting that many with the higher incidence of the disease spent more time in the sun due to the ability of the wealthy Swedes to head to warmer, more sunny climates for vacation.