Common ones include: Flushing of the skin. However, some states require a live video consultation. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. The pills are available in strengths as high as 20 mg, and hangs around your bloodstream for up to 36 hours. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Finally, we checked customer reviews to better understand user experiences with each platform. Other conditions that may disqualify you from an ED prescription include a history of stroke, kidney or liver disease, cancer, diabetes, or a bleeding disorder.Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP. Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects often last for 4 to 5 hours. It might work longer if you have mild to moderate erectile dysfunction. Vardenafil. Viagra works at its best within a few hours after it’s taken. In most people, the drug is most effective about 1 hour after it’s taken. Over time, Viagra is slowly removed from the body.