Use the oral syringe provided with your medication to measure and take your dose. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Do not take more or less of it or take it more often than prescribed by your doctor. Brand names Why is this medication prescribed? The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra.He or she will tell you how much VIAGRA to take and when to take it. Get into the mood. You will not get an erection just by taking VIAGRA. You must be sexually stimulated for it to work. Take your time. VIAGRA usually starts to work within minutes. You may take it up to 4 hours before sexual activity. · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose. 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) .