Although not all of these side effects may occur, if they do occur they may need medical attention. Side effects Side effects of oral ED medicines are often mild. Protein binding is independent of total drug concentrations. The major circulating metabolite results from N-desmethylation of sildenafil, and is itself further metabolized. It is not known if the medicine is safe for use in these patients. If you do not have a plastic syringe or spoon, ask your pharmacist for one.Who may not be able to take sildenafil. Sildenafil is not suitable for some people. To make sure it’s safe for you, speak to your doctor or pharmacist before taking sildenafil if you: have ever had an allergic reaction to sildenafil or any other medicine. have recently had a stroke, heart attack or a heart problem – your doctor should. 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. FAQs What to consider Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. .