How long does sildenafil last? For most men, sildenafil is active for around four hours, starting within 30 to 60 minutes of taking it. But 'lasting four hours' is widely misread. It does not mean a four-hour erection; it means a roughly four-hour window during which, if you are aroused, you can get and keep an erection.
What 'lasting' actually means
This is the most important point, so it is worth being blunt. Sildenafil raises the potential for an erection; it does not create a standing one. During its active window your body can respond to arousal more easily and effectively than usual, and between moments of arousal things settle as normal. An erection that simply would not go away is not the goal and is not how the medicine works; a prolonged, painful erection is a rare emergency, not the intended effect. What you are buying is a window of opportunity, not a fixed state.
How long does sildenafil take to work?
Taken on a relatively empty stomach, sildenafil is usually absorbed within 30 to 60 minutes, reaching peak levels in the blood at around one hour. That peak is when the effect is strongest. The NHS guidance on taking sildenafil is to take it about an hour before sex for exactly this reason. Take it too close to sex and it has not yet reached working levels; the common complaint that it 'did nothing' is often really that it was not given time.
Peak and taper
After peaking at about an hour, sildenafil's level in the blood gradually falls. Its half-life, the time for the level to halve, is around three to four hours according to the official prescribing information, so the effect is strongest in the first couple of hours and then tapers. By four to five hours after the dose, most of the effect has gone for most people, though there is variation between individuals. Planning around that first, stronger part of the window makes the most of a dose.
How long does 100mg sildenafil last?
Broadly the same four hours or so. The half-life does not change with the strength, so 100mg does not double the duration; a higher dose mainly makes the effect stronger within the same window, with a somewhat longer tail as levels fall from a higher peak. It also raises the likelihood of side effects such as headache, flushing and visual disturbance. If the window itself feels too short at any strength, the answer is usually a different medicine rather than a bigger dose; how the strengths are chosen is covered in our guide to sildenafil dosage.
The food and alcohol effect
Food is the single biggest practical influence on how sildenafil behaves. A large or fatty meal slows its absorption, delaying the onset and lowering the peak, so it may take longer to work and feel weaker. If you want reliable timing, take it on a relatively empty stomach, or allow extra time after a heavy meal. This is one area where tadalafil differs, as food does not meaningfully affect it; a reason some men prefer it around mealtimes.
Alcohol matters too. A drink or two is unlikely to change much, but heavier drinking works directly against the erection you are trying to have and can make the window feel shorter or emptier than it is. We cover the physiology in alcohol and erections.
If a dose seems not to have worked, food, alcohol and timing are among the first things to check; see why ED treatment might not work.
Why the window varies between people
The four-hour figure is an average, and several things stretch or shrink it. Age is one: sildenafil is cleared more slowly in older men, so levels stay higher for longer, which is partly why prescribers often start them on 25mg. Kidney or liver problems have the same effect, as do certain interacting medicines, including some antifungals, antibiotics and HIV treatments, which slow the enzyme that breaks sildenafil down.
The reverse worry, that sildenafil stops lasting as long with repeated use, has little support: PDE5 inhibitors do not show meaningful tolerance in trials, so a window that seems to be shrinking is more often explained by food, alcohol, stress or an underlying health change than by the medicine wearing out. If the pattern genuinely changes, mention it at a review rather than adjusting anything yourself.
How it compares to tadalafil
If the four-hour window feels restrictive, the obvious alternative is tadalafil, which stays active for up to 36 hours and can also be taken as a daily low dose that removes timing altogether. Neither is better in general; sildenafil's defined window suits planned occasions, while tadalafil's long window suits spontaneity. Both are prescription-only in the UK, and switching between them is a routine conversation with a prescriber rather than a fresh start.
We compare the two directly in sildenafil versus tadalafil.
The practical summary
Take sildenafil 30 to 60 minutes before you expect to have sex, ideally not straight after a heavy meal, and plan for the effect to be strongest in the first couple of hours and to fade by around four to five. Arousal is still required throughout, and how long sildenafil lasts for you personally will settle into a recognisable pattern after a few uses. Used with those expectations, it does what it is meant to; used with the wrong ones, it can seem to underperform when it is really working exactly as designed.
