This medicine is available on prescription and you can also buy it from most pharmacies. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. 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. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Prolonged erections can be dangerous. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Do not take a double dose to make up for a missed one. · Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where .  · Generic Viagra is also available through Hims starting at $4 per dose. Viagra is available in mg, mg, and mg doses and can be purchased in day and day supplies. Shipping is. VIAGRA may not be right for every man, but it has been shown to help approximately 4 out of 5 men get and keep erections hard enough for sex at doses of 50 mg or mg.* * Seventy-two percent, 80%, and 85% of the patients on 25 mg, 50 mg, and mg of VIAGRA, respectively, achieved erections hard enough for sex, compared to 50% on .