sildenafil
Viagra (sildenafil) is a PDE5 inhibitor originally from Pfizer. By blocking the enzyme that breaks down cGMP, it enhances blood flow to the penis during sexual stimulation, treating erectile dysfunction; a separate formulation (Revatio) treats pulmonary arterial hypertension.
This page is based on FDA prescribing information and the EMA medicine record for sildenafil, cross-checked with MedlinePlus and the National Cancer Institute drug dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
During sexual stimulation, the body sends a chemical message that relaxes the smooth muscle in the penis and lets blood flow in. PDE5 is the eraser that wipes that message away. Sildenafil shields the message from the eraser, so the relaxation signal lasts longer and an erection can happen.
In simple terms
Sildenafil belongs to a class called PDE5 inhibitors. During sexual stimulation, the body releases chemicals that relax the smooth muscle in the penis and let blood flow in, producing an erection. An enzyme called PDE5 normally breaks down that signal quickly. Sildenafil blocks PDE5, so the relaxation signal lasts longer and blood flow increases. Sildenafil does not cause an erection on its own; sexual stimulation is still needed.
In depth
Sildenafil is a pyrazolopyrimidinone derivative that selectively inhibits cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5) in the corpus cavernosum. By preventing cGMP degradation, sildenafil increases cGMP availability, prolonging smooth muscle relaxation, vasodilation, and blood engorgement of the corpus cavernosum during sexual stimulation. In the pulmonary vasculature the same mechanism relaxes pulmonary smooth muscle, lowering pulmonary arterial pressure; this underlies the separate Revatio indication for pulmonary arterial hypertension.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
PDE5 is the eraser that wipes that message away
- During sexual stimulation, the body sends a chemical message that relaxes the smooth muscle in the penis and lets blood flow in.
- An enzyme called PDE5 normally breaks down that signal quickly.
- Sildenafil blocks PDE5, so the relaxation signal lasts longer and blood flow increases.
- Sildenafil does not cause an erection on its own; sexual stimulation is still needed.
Target: Phosphodiesterase type 5 (PDE5)
The enzyme that breaks down cyclic GMP in smooth muscle cells of the corpus cavernosum and pulmonary vasculature; inhibiting it lets cGMP accumulate and prolongs smooth muscle relaxation and vasodilation.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- For the treatment of erectile dysfunction
Approved uses in European Union
EMA- Treatment of men with erectile dysfunction, which is the inability to achieve or maintain a penile erection sufficient for satisfactory sexual performance; sexual stimulation is required for effectiveness
Official sources
The statements on this page trace back to these records.
- U.S. Food and Drug Administration: sildenafil prescribing information
U.S. Food and Drug Administration
- Viagra (sildenafil) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- MedlinePlus: sildenafil
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: sildenafil citrate
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.