What special dietary instructions should I follow? It may be difficult to remain firm despite wanting to have sex. Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil. Do not stop taking sildenafil without talking to your doctor. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. This medicine is available on prescription and you can also buy it from most pharmacies. You can see an in-person provider or speak with a doctor virtually.$12 View other PDE5 Inhibitors Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung condition. This drug is more popular than comparable drugs. It is available in generic and brand versions. About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when. Prices for Sildenafil (Viagra) are as low as $ with a GoodRx coupon. See coupons. What are the side effects of Sildenafil (Viagra)? It’s best to take sildenafil (Viagra) about 1 hour before sex, but you can take it anywhere between 30 minutes and 4 hours before you need it. You can take sildenafil (Viagra) with or without food, but it.