The FDA is evaluating evidence of a “serious risk” of melanoma skin cancer from the following drugs:
- Adcirca (tadalafil)
- Cialis (tadalafil)
- Levitra (vardenafil)
- Revatio (sildenafil)
- Staxyn (vardenafil)
- Stendra (avanafil)
- Viagra (sildenafil)
These drugs block an enzyme called PDE5, which relaxes blood vessels and improves blood-flow to certain parts of the body. This treats erectile dysfunction and arterial hypertension.
The problem is that about 50% of melanomas also inhibit PDE5. The first studies linking PDE5-inhibition and melanoma were published in 2008. Over the next few years, studies found that PDE5-inhibition accelerated the development of melanoma and made it more invasive.
In 2014, Viagra was associated with an 84% increased risk of melanoma in a study involving 25,000 men by researchers at Harvard. The numerical risk was small — only about 9 out of 1,000 men on Viagra developed melanoma — but it made major headlines.
The result was a wave of lawsuits. Pfizer, the manufacturer of Viagra, is facing more than 80 cases in California. Dozens more lawsuits have been filed against Eli Lilly & Co., the manufacturer of Cialis.
About 76,000 Americans are diagnosed with melanoma every year — about half of them men — and Viagra has been used by millions of men. That means there could be a lot of potential lawsuits if the FDA decides the drugs need stronger warnings about melanoma.