Remove the syringe from the bottle. Avanafil Stendra. If too much is used, the chance of side effects is increased. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. Its effects often last for 4 to 5 hours. This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . Sildenafil oral tablet is used to treat erectile dysfunction (ED). It’s also used to treat pulmonary arterial hypertension (PAH). What is sildenafil? Sildenafil is a . Headache, flushing, and upset stomach are common Viagra side effects. These effects are usually mild and often resolve on their own. While rare, Viagra can .