Some people may also have ringing in their ears tinnitus or dizziness. The primary measure in the principal studies was a sexual function questionnaire the International Index of Erectile Function – IIEF administered during a 4-week treatment-free run-in period, at baseline, at follow-up visits, and at the end of double-blind, placebo-controlled, at-home treatment. Viagra had no effect on saquinavir pharmacokinetics. Never purchase ED medications from a site or service that doesn’t require a prescription and medical documentation. Psychological factors like stress, depression, or anxiety can also contribute.Key facts. Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work. VIAGRA is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or mg of sildenafil. Tablets are debossed with PFIZER on one side and VGR25, VGR50 or VGR on the other to indicate the dosage strengths. Close. Best Low Cost: GoodRx. Fastest Delivery: Blink Health.: Sesame. Sign Up Now. Key Specs. Cost: Consultation prices vary based on the prescriber; $5 generic prescriptions. .