Tadalafil Cialis. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects. Sildenafil usually should not be taken more than once every 24 hours. Take sildenafil at around the same times every day.Cialis is only available by prescription in the United States. Viagra: Additionally, a study from Trusted Source. found that combining L-arginine and sildenafil (Viagra) worked better for. In most males,* Viagra works within 1 hour after it’s taken. It’s possible that Viagra can begin working within 30 minutes of being taken. But other times, it may take up to 4 hours to start. Viagra Coupons, Prices, and Savings Card. Generic Names: Sildenafil Citrate. Brand Names: Revatio. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn more about Viagra oral. 1. This is a generic drug. Even if this drug is covered by Medicare or your insurance, we recommend you compare prices.