Short answer: Sildenafil has a half-life of about 4 hours. Levels peak about 1 hour (30 to 120 minutes) after a dose. People vary, so treat these as estimates.
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. It is sold as Viagra for erectile dysfunction, as Revatio for pulmonary arterial hypertension, and as generic tablets.
Also known as: Viagra, Revatio.
Viagra comes as 25 mg, 50 mg and 100 mg tablets. Revatio comes as 20 mg tablets and as an injection for intravenous use.
The FDA Viagra label approves sildenafil for erectile dysfunction (ED). For most people the label dose is 50 mg taken as needed about 1 hour before sex (anywhere from 30 minutes to 4 hours before), adjusted to 25 mg or up to 100 mg, no more than once a day. The Revatio label approves it for pulmonary arterial hypertension in adults at 20 mg three times a day, which may be raised to up to 80 mg three times a day.
Sildenafil must not be taken with nitrates or with riociguat, because blood pressure can drop sharply. With alpha-blockers the label says to be stable on the alpha-blocker first and start at 25 mg; with ritonavir, no more than 25 mg in 48 hours. An erection lasting more than 4 hours needs emergency care. See also tadalafil, the longer-acting PDE5 inhibitor.
The FDA Viagra label says peak levels come 30 to 120 minutes after a dose on an empty stomach (median 60 minutes), and that sildenafil and its active metabolite both have a terminal half-life of about 4 hours. A high-fat meal delays the peak by about 60 minutes and lowers it by 29%. Bioavailability by mouth is about 41%.
Numbers shown are taken from the source above. Half-life varies from person to person.
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