tadalafil
Cialis (tadalafil) is a PDE5 inhibitor from Eli Lilly. By blocking the enzyme that breaks down cGMP, it enhances blood flow to the penis during sexual stimulation for erectile dysfunction, and it also relaxes smooth muscle in the prostate and bladder to relieve symptoms of benign prostatic hyperplasia.
This page is based on FDA prescribing information and the EMA medicine record for tadalafil, 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. Tadalafil shields the message from the eraser for up to 36 hours, so the relaxation signal lasts much longer than with most other medicines in this class.
In simple terms
Tadalafil 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. Tadalafil blocks PDE5, so the relaxation signal lasts longer and blood flow increases. Tadalafil is known for its long duration of action, which can last up to 36 hours. It does not cause an erection on its own; sexual stimulation is still needed. In the prostate and bladder, the same mechanism relaxes smooth muscle, easing urinary symptoms of benign prostatic hyperplasia.
In depth
Tadalafil is a carboline-based compound that selectively inhibits cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), preventing degradation of cGMP in the smooth muscle of the corpus cavernosum and corpus spongiosum of the penis. Inhibition of cGMP degradation results in prolonged smooth muscle relaxation, vasodilation, and blood engorgement, producing penile erection during sexual stimulation. In the prostate and bladder, PDE5 inhibition relaxes smooth muscle, improving urinary symptoms of benign prostatic hyperplasia. Tadalafil has a half-life of approximately 17.5 hours, supporting a window of efficacy of up to 36 hours.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
How tadalafil shields the message from the eraser
- 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.
- Tadalafil blocks PDE5, so the relaxation signal lasts longer and blood flow increases.
- Tadalafil is known for its long duration of action, which can last up to 36 hours.
Target: Phosphodiesterase type 5 (PDE5)
The enzyme that breaks down cyclic GMP in smooth muscle cells of the corpus cavernosum, prostate, and bladder; 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
- For the treatment of the signs and symptoms of benign prostatic hyperplasia
- For the treatment of erectile dysfunction and the signs and symptoms of benign prostatic hyperplasia
Approved uses in European Union
EMA- Treatment of erectile dysfunction; sexual stimulation is required for effectiveness
Official sources
The statements on this page trace back to these records.
- U.S. Food and Drug Administration: tadalafil prescribing information
U.S. Food and Drug Administration
- Cialis (tadalafil) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- MedlinePlus: tadalafil
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: tadalafil
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.