It’s available in 25 mg, 50 mg, and mg tablets and lasts up to 18 hours. Yes, ED pills can cause side effects. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue. Refills: See if you can set up automatic refills or order as needed. ED medications can cause side effects, and it’s crucial to have access to a medical provider if needed. You can get a prescription online following a quick and easy visit with a member of our clinical team.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. Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. Consumer Reports Best Buy Drugs shares how you might be able to get generic Viagra, known as sildenafil, at a much lower price.