How long does Viagra last?

Viagra (sildenafil) works for about 4 hours. Its label says you can take it anywhere from 30 minutes to 4 hours before sex, and sildenafil leaves your blood with a half-life of about 4 hours. Cialis (tadalafil) lasts far longer: in its label’s trial it still improved erections 36 hours after a dose. Vardenafil and avanafil sit close to Viagra, at roughly 4 to 5 hours.

“Lasting” means the window in which the pill can help, not an erection that lasts for hours. Every one of these drugs needs sexual stimulation to work, and an erection that won’t go down after 4 hours is a medical emergency. Here is what each label says about timing, and what changes it.

The timing at a glance

These figures come from each drug’s FDA label. Time to peak is the median after a single dose on an empty stomach.

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Half-life is the time it takes for the level in your blood to fall by half. It is a rough guide to the window, not a stopwatch: the effect fades as the level falls, and how fast that matters for you depends on your dose and your body.

How long Viagra lasts

The Viagra label sets the usual dose at 50 mg about an hour before sex, and allows it anywhere from 30 minutes to 4 hours before. On an empty stomach, sildenafil reaches its peak level in 30 to 120 minutes, with a median of 60 minutes. Both sildenafil and its main active breakdown product have a half-life of about 4 hours.

In practice, that gives most men a window of a few hours that opens somewhere between 30 minutes and an hour after the pill. In the label’s four trials of 1,797 men, 63% at 25 mg, 74% at 50 mg and 82% at 100 mg reported improved erections, against 24% on placebo.

Generic sildenafil is the same drug. The FDA requires a generic to deliver the same amount of sildenafil to the body as the brand, so the timing is the same whichever you take.

How long Cialis lasts

Tadalafil is the long-acting option. The Cialis label reports a mean half-life of 17.5 hours in healthy men, and says that as-needed Cialis “was shown to improve erectile function compared to placebo up to 36 hours following dosing.” In the trial behind that statement, 64% of men taking 20 mg had successful intercourse 33 to 39 hours after the dose, against 37% on placebo. At 22 to 26 hours, the figure was 61%.

Tadalafil peaks more slowly than sildenafil, at a median of 2 hours, and food doesn’t change how much you absorb. That is why many men who want to skip the planning choose it.

Daily Cialis works differently again. A 2.5 mg or 5 mg tablet taken at about the same time every day keeps a steady level in your blood, so you don’t time a pill around sex at all. See sildenafil vs tadalafil for how the two compare on side effects and cost.

Vardenafil and avanafil

Vardenafil (sold as Levitra, now discontinued, and as generics) is taken about 60 minutes before sex. It peaks at a median of 60 minutes and has a half-life of about 4 to 5 hours, much like sildenafil.

Avanafil (Stendra) is the fastest to start. Its label allows the 100 mg and 200 mg doses as early as about 15 minutes before sex, and the 50 mg dose about 30 minutes before. It peaks in 30 to 45 minutes and has a half-life of about 5 hours. Few online providers in our comparison sell it.

What changes how long it lasts

Food

A heavy, high-fat meal slows sildenafil. The label reports that it delays the peak by about 60 minutes and lowers it by 29%. Vardenafil’s peak falls by 18% to 50% after a high-fat meal, and avanafil’s by about 39%, with the peak about an hour later. Tadalafil is the exception: the label says food doesn’t change how fast or how much is absorbed. If Viagra seems slow after dinner, taking it on a lighter stomach is the label’s own explanation.

Age, liver and kidneys

Your body clears these drugs more slowly as you age and if your liver or kidneys don’t work well, so levels run higher for longer. The Viagra label suggests a 25 mg starting dose for men over 65, for men with any degree of liver impairment and for men with severe kidney impairment, where exposure to sildenafil roughly doubles.

Other medicines

Some medicines block the liver enzyme (CYP3A4) that breaks these drugs down, which raises their levels and stretches how long they last. With ritonavir, the Viagra label caps sildenafil at a single 25 mg dose in 48 hours, because ritonavir raises sildenafil exposure about 11-fold. With strong inhibitors such as ketoconazole or ritonavir, the Cialis label caps as-needed tadalafil at 10 mg, no more than once every 72 hours.

When an erection lasts too long

An erection that lasts more than 4 hours is called priapism, and every one of these labels tells you to get emergency care if it happens. Left untreated, it can permanently damage the penis. It is rare, but it is the one situation where “it lasts longer” is a problem rather than a benefit.

The long half-life matters for safety too. Never take any of these drugs with nitrates, such as nitroglycerin or “poppers”: together they can drop your blood pressure dangerously. Because tadalafil stays in the body so long, the Cialis label says at least 48 hours should pass after your last dose before a doctor gives a nitrate in an emergency. Tell any emergency team which ED drug you took and when.

Taking it more often doesn’t make it last longer

The labels limit sildenafil, tadalafil (as needed), vardenafil and avanafil to one dose a day. A second pill doesn’t extend the window; it raises your level and your risk of side effects such as headache, flushing and, rarely, a dangerous drop in blood pressure. If the window feels too short, the options are a different drug (tadalafil), daily tadalafil, or a dose change your clinician agrees to.

What it costs to get one online

All four drugs need a prescription, and licensed telehealth providers can prescribe them after an online review. As of October 2026, generic sildenafil costs $1.60 to $6.25 a dose at the online providers that publish a regular per-dose or per-pack price, and daily generic tadalafil is $40 a month on Hims’ monthly plan. Prices usually rise with strength, so check the price for the dose you’re prescribed.

Compare providers on our ED rankings, generic sildenafil list and daily tadalafil list, or start from the ED hub. For the full price picture, see where generic Viagra is cheapest.

The bottom line

Viagra lasts about 4 hours, opening 30 minutes to an hour after you take it, and a heavy meal can push that back. Cialis covers up to 36 hours from one dose, or all the time on a daily tablet. Vardenafil matches Viagra, and avanafil starts fastest. None of them works without arousal, and an erection lasting more than 4 hours needs emergency care. A licensed clinician can match the drug and dose to how you want to use it.