Generic versions of sildenafil, vardenafil and tadalafil are available. For the best results swallow the medication whole with water on an empty stomach one hour before sexual activity as food will slow down the absorption of Sildenafil and meaning it will take slightly longer to work. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Eating an hour after taking the pill will not affect its activity. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly.$ (save %) local_offer_outlined Avg retail price $ medication_outlined Availability Available See GoodRx coupons warning Are you looking . Brand-name vs. generic Reducing long-term drug costs Financial assistance Next steps Viagra (sildenafil) is a brand-name oral tablet prescribed for erectile . Quantity Manufacturer’s Savings Card Sponsored You may be eligible to save up to 50% on your brand-name prescription * * Terms and Conditions Apply Get Savings Card .