If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food.Sildenafil Coupon Simply bring the coupon below to the pharmacy, and save on Sildenafil at CVS, Walgreens, Walmart, Safeway, Albertsons, Rite Aid, Target, Kroger, and many . This means that 4 hours after you take a dose, your body has cleared half of the dose. In most cases, it takes about 5 half-lives for your body to completely remove a drug from your system. So. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide.