The short answer: tadalafil works the same way as sildenafil, by blocking the enzyme PDE5 so that blood vessels in the penis relax more fully during arousal. The difference is time. Tadalafil is cleared from the body much more slowly, so a single dose can remain active for up to 36 hours, and that opens up a dosing option sildenafil cannot offer: a small daily tablet.
What is tadalafil?
Tadalafil is a medicine used to treat erectile dysfunction, and it is also licensed for benign prostate enlargement and, at specialist doses, for pulmonary hypertension. It is a PDE5 inhibitor, the same class as sildenafil, and is now widely available as a generic since the original branded tablet lost patent protection. The NHS lists tadalafil as a treatment for erection problems, taken either before sex or as a daily tablet. For erectile dysfunction the as-needed strengths are usually 10mg and 20mg, while the daily option is a lower 2.5mg or 5mg dose.
The same mechanism, briefly
An erection depends on a messenger molecule called cGMP, which relaxes the smooth muscle in the penile arteries and lets blood flow in. An enzyme called PDE5 breaks cGMP down and switches the response off. Tadalafil inhibits PDE5, so when arousal starts the signal, the response is stronger and lasts longer. Like all medicines in this class, it needs arousal to do anything; it does not create an erection on its own.
If you want the mechanism in full detail, our explainer on how sildenafil works covers the same biology step by step.
Why 36 hours matters
Sildenafil is active for around 4 hours, which means sex needs to happen inside a window you planned for. Tadalafil has a much longer half-life, around 17.5 hours, which means meaningful levels stay in the blood for up to a day and a half. Within that period, you can respond to arousal whenever it happens, without watching the clock.
For many men, that is the main appeal: it separates taking a tablet from the moment itself, which removes a source of pressure. The trade-off is that the medicine, including any side effects such as muscle aches or indigestion, is also in your system for longer.
As-needed or daily: two ways to take it
Tadalafil is licensed in two patterns. Taken as needed, a higher dose is used at least 30 minutes before sex, and the long window does the rest. Taken daily, a much lower dose keeps a steady, modest level in the blood at all times, so there is no timing to think about at all. Daily dosing tends to suit men who have sex more than twice a week or who simply want spontaneity back.
Choosing between these patterns is a genuine decision with trade-offs, which we walk through in daily versus as-needed ED treatment.
How long does tadalafil take to work?
Taken as needed, tadalafil usually starts to work within 30 to 60 minutes, and because it lasts so long there is less need to time the dose precisely to a planned moment. The daily version works differently: rather than waiting for a single dose, you build up a steady level over several days, so it typically reaches its full effect after about four or five days of consistent use. That is worth knowing, because a daily tablet judged on its first day can seem underwhelming before it has had time to establish itself.
Does tadalafil work for everyone?
For most men with erectile dysfunction, tadalafil helps, but it shares the limits of the whole PDE5 class. It needs arousal to work, it manages the symptom rather than curing the underlying cause, and a minority of men respond poorly and need a dose change, a switch to a different medicine, or investigation of a cause the tablet cannot fix. A disappointing first attempt is common and rarely means the treatment has failed; how well it works depends on arousal, the dose and giving it a fair trial. If you are still choosing, our comparison of sildenafil versus tadalafil sets out the practical differences side by side.
Food, alcohol and practicalities
Unlike sildenafil, tadalafil's absorption is not meaningfully affected by food, so it can be taken with or after a meal without losing effect. The manufacturer's product information confirms that food and modest alcohol do not require dose changes. Heavier drinking, though, works against erections in its own right and can add to blood-pressure effects.
Common side effects
Tadalafil's side effects mirror the rest of its class: headache, flushing, a blocked nose and indigestion, all stemming from blood vessels relaxing beyond the intended target. It is somewhat more associated with back pain and muscle aches than sildenafil, typically appearing a day or so after a dose and settling on their own. Because the medicine stays in the body longer, any side effect that does occur may also linger longer. Most men find the effects mild; if they are not, the dose, the pattern or the medicine itself can be changed at review.
Prescription-only, and why
Tadalafil is a prescription-only medicine in the UK. A prescriber checks your cardiovascular health, blood pressure and full medicine list first, because erectile dysfunction can signal underlying vascular disease and because interactions, particularly with nitrates and some prostate or blood pressure medicines, are genuinely dangerous rather than theoretical. Treatment is then reviewed to make sure the dose and pattern suit you.
