PDE-5 inhibitors taken as needed are usually the first drugs prescribed for erectile dysfunction (ED). They are relatively safe, easy to take, and very likely to improve ED symptoms. They improve erections by increasing blood flow in the penis.
PDE-5 inhibitors include avanafil (Stendra), sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra, Staxyn). Avanafil, sildenafil and vardenafil are taken on demand and are active for 4 to 6 hours. Tadalafil can be taken once daily or on demand and is active for up to 36 hours. Although most men respond the first or second time the drug is taken, some men need to take it on 6 to 8 different occasions before it begins to work.
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