Important: this page is educational. Tadalafil is a prescription drug and requires a clinician evaluation, especially to screen for nitrate use and cardiovascular risk.
What is tadalafil?
Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor sold as Cialis. Its defining feature is a long half-life of roughly 17.5 hours, which produces clinical effects for up to 36 hours after a single dose. It earned the nickname "the weekender" for that reason.
How does tadalafil work?
Sexual arousal triggers nitric oxide release in the penis, which raises cyclic GMP and relaxes the smooth muscle of the corpus cavernosum, allowing blood flow and erection. PDE5 breaks down cyclic GMP. By inhibiting PDE5, tadalafil prolongs the cyclic GMP signal and supports a firmer, more reliable erection in response to arousal. The drug does not create erections on its own; sexual stimulation is still required.
PDE5 is also expressed in pulmonary and systemic vasculature and in the prostate, which is why tadalafil has additional approved uses in BPH and pulmonary hypertension.
How is tadalafil dosed?
Two dosing patterns dominate. On-demand dosing uses 10 to 20 mg taken roughly one to two hours before sexual activity, with effect lasting up to 36 hours. Daily low-dose uses 2.5 to 5 mg taken every day at the same time, which produces steady plasma levels and removes the need for timing around intimacy.
Daily low-dose tadalafil also treats lower urinary tract symptoms from BPH and may provide endothelial benefits in men with metabolic or cardiovascular risk factors. Read more in the daily Cialis breakdown.
How long until tadalafil works?
On-demand effect begins in roughly 30 to 45 minutes and is reliable by two hours. Daily dosing reaches steady state in about five days; full effect on erectile function and urinary symptoms develops over two to four weeks.
Side effects of tadalafil
Common side effects include headache, flushing, nasal congestion, indigestion, and back pain or muscle aches that typically appear 12 to 24 hours after dosing. Most are mild and resolve as the body adapts or with lower dosing.
Rare but serious effects include sudden vision loss (non-arteritic anterior ischemic optic neuropathy), sudden hearing loss, and priapism (erection lasting more than four hours). Any of these is a reason to seek emergency care.
Who should not take tadalafil?
Absolute contraindications include current or recent nitrate use and known severe hypersensitivity. Use caution with alpha-blockers for BPH (start at the lowest tadalafil dose), significant hepatic or renal impairment, recent stroke or myocardial infarction, unstable angina, severe heart failure, and uncontrolled hypertension or hypotension. Strong CYP3A4 inhibitors raise tadalafil exposure and may require dose adjustment.
For younger men with new erectile changes, read ED in your 30s for context on root causes.
Tadalafil vs sildenafil
Sildenafil has a four-hour half-life and faster onset on an empty stomach. Tadalafil has a 36-hour window and is less affected by food. Men who want spontaneity or daily benefit typically prefer tadalafil; men who want a short focused effect often prefer sildenafil. Both work well when matched to lifestyle and goals.