How Does Viagra Work?
Viagra (sildenafil) is a PDE5 inhibitor. During sexual stimulation, it helps relax blood vessels in the penis, allowing increased blood flow. It does not create an erection on its own — arousal and stimulation are still required.
Written by Virantus Editorial Team
Medically reviewed by Virantus Clinical Team · Reviewed August 2026
Last updated August 2026
The mechanism
An erection depends on blood flowing into the penis and staying there. Sildenafil blocks an enzyme (PDE5) that normally limits blood flow. With sexual stimulation, that can make it easier to get and maintain an erection.
Sildenafil does not increase desire. It does not work without stimulation. It is not an aphrodisiac.
Timing and duration
Most men take sildenafil about 30–60 minutes before sexual activity. Effects typically last about 4–6 hours. High-fat meals can delay absorption for many men.
A clinician determines whether sildenafil is appropriate and what dose fits your health profile.
When it may not work
Sildenafil may not work if the underlying cause of ED is primarily psychological without addressing stress or relationship factors, if nerve or blood-vessel damage is severe, or if drug interactions make it unsafe. Evaluation helps distinguish treatable causes from situations that need a different approach.
Common questions
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