Magnotti will be happy to go over your list in a meeting. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. When a man becomes aroused the brain sends a signal to the cells in the penis to release nitric oxide, which turns on the production of cGMP. Sildenafil Viagra. If you do not have a plastic syringe or spoon, ask your pharmacist for one. · Take sildenafil exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets. Revatio is . 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. If you’re prescribed Viagra, you can purchase it in doses of 25, 50, or milligrams (mg). Your doctor may prescribe Viagra if they decide it’s the safest treatment option based on your.