Sildenafil may cause side effects. You can take this medicine with or without food 30 minutes before sex, depending on the dose. One of the messengers released when you’re aroused is called cyclic GMP. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This patent was published in and expired in This site is intended only for U.Oral medications are a successful erectile dysfunction treatment for many men. They include: Sildenafil (Viagra) Tadalafil (Adcirca, Cialis) Vardenafil (Levitra, Staxyn) Avanafil (Stendra) All four medications enhance the effects of nitric oxide — a natural chemical your body produces that relaxes muscles in the penis. AdFree 2-day Shipping On Millions of Items. No Membership Fee. Shop Now! AdDon’t go to the pharmacy without checking prices at GoodRx® first. No commitment or fees. Find the lowest price in your neighborhood & use our free coupons to save up to 80%.