At the same time, on-treatment function was better in treated patients who were less impaired at baseline. This is consistent with ritonavir’s marked effects on a broad range of P substrates. Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss. The major circulating metabolite results from N-desmethylation of sildenafil, and is itself further metabolized. Rarely reported side effects include: an erection that will not go away priapism.What Happened When I Took Viagra Recreationally. 1. Viagra was effective for much longer than four hours. Shutterstock. Viagra comes in three different sizes: 25mg, 50mg, or mg. In the past, I’ve found that 25mg always did the job just fine. However, my journey begins with a bottle of the mg tabs which I’ve chosen to cut into thirds. Find patient medical information for Viagra oral on MD including its uses, side effects and safety, interactions, pictures, warnings and user ratings. 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.