Some medications should not be taken with sildenafil. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Sildenafil may not be safe to take for people with certain medical conditions including: a past history of stroke or heart attack in the last 6 months retinitis pigmentosa an eye disease It can also interact with many other medicines, particularly nitrates used in heart disease , amyl nitrite and blood pressure medicines.7 Over The Counter Medications for ED. Depending on the cause of erectile dysfunction, the most effective treatment can vary. Typically, the best way to treat erectile dysfunction is to address the underlying cause. Second is by using oral medications like Viagra® (sildenafil), Cialis® (tadalafil), or Levitra® (vardenafil), all of which are. Causes of ED. There are several medications and treatments used to treat erectile dysfunction (ED, impotency), including Viagra (sildenafil), testosterone replacement . There are also a few OTC alternatives to Viagra that may be worth exploring as well. Takeaway Generic Viagra, or sildenafil citrate, works the same as Viagra, but at a lower cost.