How Long Does Sildenafil Last? What Trials Found at 1, 4, 8 and 12 Hours

"How long does sildenafil last" is really five questions. How soon it starts working. How long the window lasts in which it can help you get an erection. How long a single erection lasts once you have one. How long the drug stays in your body. And how soon you can take another tablet. Each has a different answer, and most pages blur them together.

This guide answers each one from the evidence: the FDA and EU prescribing information for Viagra, and the small number of trials that tested it at set times after the dose, from 14 minutes up to 12 hours, using stopwatches, rigidity monitors, self-ratings and diaries. Some of those numbers are longer than the label suggests. We explain why, and why you should still plan around the label.

The short answer

Sildenafil reaches peak blood levels 30 to 120 minutes after a dose, with a median of about 60 minutes on an empty stomach. Its half-life is about 4 hours. The FDA label says to take it about an hour before sex, anywhere from 30 minutes to 4 hours beforehand, and no more than once a day.

That 4 hour window is where the effect is strongest, not where it stops. In a crossover trial, men who took 100 mg still had erections more than twice as long as on placebo when stimulation began 12 hours after the dose. In an open-label study of men who already responded to sildenafil, 74% had successful sex 12 hours after taking it. The effect fades steadily over that time, so the realistic answer is: strong for about 4 hours, weaker but often still present up to 8 to 12 hours, and mostly cleared from the body within a day.

Five questions hiding in one

What you are asking	Answer	Where it comes from
How soon does it start working?	As early as 12 to 14 minutes in some men; median 25 to 36 minutes in trials	EU prescribing information; Eardley 2002; Padma-Nathan 2003
How long is the window?	Strongest in the first 2 hours, reduced at 4 hours, measurable up to 12 hours	FDA label section 12.2; Gingell 2004; Moncada 2004
How long does an erection last?	It helps you get and keep an erection during stimulation, usually until ejaculation; it does not create one on its own or guarantee one for the whole time	FDA label section 12.1; Ekmekcioglu 2005
How long does it stay in the body?	Half-life about 4 hours; at 24 hours levels are under 0.5% of the peak in healthy men	FDA label section 12.2 and 12.3
When can I take another?	The label limit is once per day; waiting a full 24 hours is the simple way to keep to it	FDA label section 2.1

What happens in your body, hour by hour

Sildenafil is absorbed quickly, but only about 41% of each dose reaches the bloodstream (the range across people is 25% to 63%). The liver breaks it down, mainly through an enzyme called CYP3A4, into a metabolite called N-desmethyl sildenafil. That metabolite also blocks PDE5, at about half the strength of the parent drug. Its blood levels run at about 40% of sildenafil's, so the label estimates it provides about 20% of the overall effect. Both have a half-life of about 4 hours, which is why the metabolite does not stretch the effect much beyond the parent drug.

Time after a 100 mg dose	What is going on
0 to 30 minutes	Absorption starts. Many men already respond: about half of previous responders within 20 minutes in one study, 71% within 30 minutes in another
30 to 120 minutes	Peak blood level, median about 60 minutes when fasted, roughly 440 ng/mL after 100 mg
1 to 2 hours	Strongest effect in the studies that compared time points
About 4 hours	Levels well down from the peak. Effect still present but clearly weaker than at 2 hours
8 hours	Levels well below the peak. Trials still found a benefit in many men
12 hours	Lower again. Smaller but measurable benefit in trials
24 hours	About 2 ng/mL in healthy volunteers, under 0.5% of the peak

The peak and 24 hour levels are measured values from the FDA label. The effects at each time point come from the trials below.

How fast sildenafil starts working

The label's "about an hour before" advice is conservative. Two published studies timed onset directly.

The larger was a stopwatch study of 228 men who had already used sildenafil 100 mg successfully for at least two months. They took the tablet at least two hours after eating, started a stopwatch and recorded when they first had an erection that led to successful intercourse.

Time after dose	Sildenafil 100 mg (n=115)	Placebo (n=113)
Within 14 minutes	35%	22%
Within 20 minutes	51%	30%
Median time to success	36 minutes	141 minutes

A laboratory study with a rigidity monitor points the same way. Seventeen men with ED of no known physical cause took 50 mg and watched erotic video. The median time to an erection was 27 minutes, with the fastest at 12 minutes. 71% responded within 30 minutes and 82% within 45 minutes. The EU prescribing information summarises an onset study with a median of 25 minutes and a range of 12 to 37 minutes. It is likely the same manufacturer study reported with a different cut-off, so treat it as confirmation rather than extra evidence.

Placebo numbers matter here. Almost a third of placebo users in the stopwatch study also succeeded within 20 minutes, probably because these were men used to succeeding. The drug adds to what arousal already does. It does not replace it.

How long the effect window lasts

The FDA label describes one study of the time course and summarises it in a sentence: an effect for up to 4 hours, but the response was diminished compared to 2 hours. The EU prescribing information describes a study in which sildenafil still produced an erection 4 to 5 hours after the dose.

A published study with 2 and 4 hour data, probably the same one the labels summarise, gives the detail. Sixteen men took 100 mg or placebo, and 60 minutes of erotic stimulation started either 2 or 4 hours later. When stimulation started at 2 hours, the median time the men rated their erection hard enough for penetration was 19.5 minutes on sildenafil against 0 on placebo. At 4 hours it was 5 minutes against 0. Still working, but much less.

Stimulation started (Eardley 2002, study II)	Sildenafil 100 mg, median self-rated minutes of usable erection	Placebo
2 hours after the dose	19.5 (range 0 to 55)	0 (range 0 to 23)
4 hours after the dose	5 (range 0 to 45)	0 (range 0 to 27)

The wide ranges are the point. Some men had nothing at 4 hours and some still had 45 minutes. Duration varies a lot from one man to the next.

What happened at 8 and 12 hours

A 2004 crossover trial went further. Sixteen men aged 36 to 68, with ED of no known physical cause, took 100 mg or placebo 1, 8 or 12 hours before erotic stimulation. Erections were measured by a device that records rigidity, and the men also rated them.

Stimulation started	Measured minutes at 60% rigidity or more	Self-reported minutes hard enough for penetration
Placebo	3	7
1 hour after sildenafil	26	33
8 hours after sildenafil	11	23
12 hours after sildenafil	8	16

Of the men who responded at 1 hour (69% of the group), 82% still responded at 8 hours and 45% at 12 hours. By 12 hours, fewer than half of the responders were still responding.

Two at-home studies add real-world numbers. In an open-label study, 40 men who had responded to sildenafil before were given eight 100 mg doses. On four occasions they attempted sex at both 1 and 12 hours after dosing, and on four more at 12 hours only. Of the 34 who finished, 97% had successful intercourse at 1 hour and 74% at 12 hours.

In a second study of 48 satisfied sildenafil users, the timing between dose and sex ranged from under half an hour to more than 10 hours. Getting an erection hard enough for penetration did not depend on timing. Keeping it long enough to finish intercourse did: success peaked at 92.8% at 1.5 to 2 hours and fell to 81.6% beyond 10 hours.

Why you should still plan around 4 hours

The 8 and 12 hour results are real, but they come with limits that matter if you are deciding when to take a tablet.

• Small groups. The laboratory studies had 16 men each. The largest 12 hour study had 34.
• Men who already respond. Two of the studies enrolled only men known to respond to sildenafil. Men with harder-to-treat ED, such as after prostate surgery or with long-standing diabetes, were not tested this way.
• Mostly at 100 mg. The two 12 hour studies with a stated dose used 100 mg; none tested 25 or 50 mg at 8 or 12 hours.
• No placebo in the 12 hour home study. Without a placebo arm, some of that 74% may have happened anyway in men used to success.
• The effect fades. In every study, results at 8 or 12 hours were below those at 1 or 2 hours.

The practical reading: if sex happens later than planned, the tablet may well still help, so there is no reason to take another. But if you want the best chance of success, the first 1 to 4 hours are the window the evidence supports most strongly.

How long an erection lasts on sildenafil

Sildenafil does not produce an erection that lasts for hours. It makes it easier to get and keep an erection in response to sexual stimulation, usually until ejaculation, though it does not guarantee an erection for as long as stimulation lasts. The FDA label is explicit that at recommended doses it has no effect without sexual stimulation.

After orgasm, the erection fades as it normally would, though slightly more slowly. In a laboratory study of healthy volunteers, the time for rigidity to fall away after ejaculation was 3.1 minutes on sildenafil against 1.93 minutes on placebo. The same research found ejaculation took somewhat longer on sildenafil: 3.89 against 2.23 minutes in the first group of 30 men and 4.91 against 2.23 in the second.

An erection that will not go down is not a sign the drug is working well. The label says to get medical help for any erection lasting more than 4 hours. Priapism, a painful erection lasting over 6 hours, can permanently damage the penis if it is not treated quickly.

Can you go again after ejaculating?

This is the question most men are really asking. The evidence is thin and mixed. All three studies were in men without ED, so the results may not carry over to men who need the drug.

Study	Who	Dose	Finding
Aversa 2000	20 healthy men, mean age 32, continuous erotic stimulus	100 mg	Time until a new erection after ejaculation: 2.6 minutes on sildenafil against 10.8 minutes on placebo
Mondaini 2003	60 healthy men aged 20 to 40, at home	25 mg	12 of 30 on sildenafil reported a shorter recovery time against 4 of 30 on placebo; erection quality did not improve
Ekmekcioglu 2005	30 healthy volunteers, laboratory, stimulation continued after ejaculation	Not stated in abstract	Time to best rigidity after ejaculation: 15.66 minutes on sildenafil against 19.10 on placebo; the difference was not statistically significant

Two of three studies found a shorter recovery time and one did not. What is consistent is that the drug is still active for a while after ejaculation, so a second erection with renewed stimulation is possible within the same window. It is not guaranteed, and it is not a reason to take a second tablet: the label limit is once a day.

If your concern is finishing too early rather than getting an erection, sildenafil is not approved for premature ejaculation. Our sildenafil and dapoxetine guide covers the combination products sold for that purpose.

Does 100 mg last longer than 50 mg?

The label says sildenafil's pharmacokinetics are dose proportional over the recommended range. In plain terms, 100 mg gives about double the blood level of 50 mg at every point in time, and the half-life stays at about 4 hours.

Doubling the starting level means it takes one extra half-life, about 4 hours, for the level to fall back to any given point. So a higher dose keeps levels higher for longer. The label also says the erection response measured in the laboratory rose with dose and blood level.

What no study has done is compare usable duration at 50 mg against 100 mg directly. The 8 and 12 hour studies with a stated dose used 100 mg. The trade-off is side effects. From 50 to 100 mg, headache, indigestion, nasal congestion and vision changes all rise, while flushing stays about the same (19% and 18%), and our sildenafil guide sets the benefit of each step against its cost. Moving to 100 mg to buy a longer window only makes sense if 50 mg is otherwise working for you and your doctor agrees.

Food and meal timing

A high fat meal delays the peak by about an hour on average and lowers it by 29%. That is a slower, somewhat weaker start, not a shorter window.

In real life the effect may matter less than the label suggests. In the study of 48 satisfied users mentioned above, taking the tablet an hour before a meal or with the meal made no significant difference compared with the usual timing of 30 to 60 minutes before sex. Successful intercourse was 84.7% when the tablet was taken an hour before a meal and 83.4% when taken with the meal, against 85.9% and 87.5% on the usual timing in the matching comparisons. The men ate what they normally ate.

If a heavy meal is part of the evening, taking the tablet on an emptier stomach an hour or two before eating is the simplest fix. Doubling the dose is not.

Oral jelly, chewables and dissolving tablets

Many men buy jelly or chewable forms because they believe they work faster. The regulator-reviewed data on dissolving sildenafil come from Viagra's orodispersible tablet in the EU. Taken without water, it was bioequivalent to the ordinary tablet in 36 healthy men aged 45 or older, meaning the same overall exposure and peak level within regulatory limits. That gives no reason to expect a faster start or a longer effect. Taken with water, the peak was 14% lower.

Food hits the dissolving form harder. After a high fat meal, the peak arrived about 3.4 hours later and was about 59% lower than when fasting. For the film-coated tablet the figures are about 1 hour and 29%.

Chewable sildenafil tablets made by other companies have been tested in two published studies, and both were bioequivalent to film-coated tablets: again, the same blood levels. Kamagra Oral Jelly and chewables such as Fildena CT are not approved in the US, UK or EU, and we found no published bioequivalence study of those specific products. There is no evidence that any of these forms last longer. Our Kamagra types comparison goes through each form.

Why sildenafil lasts longer in some men

Anything that slows sildenafil's clearance keeps it in the body longer and raises its level. The FDA label lists the groups where this happens and recommends considering a 25 mg starting dose in each of them.

Group	Increase in total exposure (AUC)	Other detail from the label
Age 65 and over	About 84%	Unbound drug about 45% higher
Liver impairment (Child-Pugh A or B)	85%	Peak 47% higher; severe impairment not studied
Severe kidney impairment (creatinine clearance under 30 mL/min)	About double	Peak about double; mild or moderate impairment made no difference
Erythromycin	182%	Peak 160% higher
Saquinavir	210%	Peak 140% higher
Ritonavir	About 11 times	Peak 4 times higher; about 200 ng/mL still present at 24 hours, against about 5 ng/mL without ritonavir in the same study

The label summarises it this way: in older men, men with liver problems or severe kidney problems, and men taking erythromycin or strong CYP3A4 inhibitors, sildenafil levels at 24 hours were 3 to 8 times higher than in healthy volunteers. For ritonavir the label goes further and limits sildenafil to a single 25 mg dose in any 48 hour period.

Longer here means a higher risk of side effects, and probably a longer period of lowered blood pressure, not a better result. It is the reason the safe use guide starts these groups at 25 mg.

How long sildenafil stays in your system

A common rule of thumb in pharmacology is that a drug is largely cleared after four to five half-lives. For sildenafil that is roughly 16 to 20 hours. The label's measured value fits: 24 hours after 100 mg, healthy volunteers had about 2 ng/mL left, against a peak of about 440 ng/mL.

About 80% of a dose leaves the body in the stool and about 13% in the urine, almost all of it as metabolites. Because the drug is about 96% bound to blood proteins, the label says dialysis is not expected to speed up its removal.

Sildenafil is a prescription medicine in most countries (the UK also allows a 50 mg pharmacy product), not a controlled substance. Routine workplace drug screens look for drugs of abuse such as opioids, cannabis, cocaine and amphetamines, not ED medicines.

When you can take the next dose

The label limit is one dose per day. That holds even if the first dose seemed to wear off, and even after the refractory period. A second tablet on the same day adds side effects and blood pressure effects without a tested benefit.

If sildenafil at a proper dose and timing does not last long enough for you, the options are a dose change agreed with a doctor, or a longer-acting drug. Tadalafil has a half-life of about 17.5 hours, and its label supports sex up to 36 hours after a dose.

Nitrates and the 24 hour question

Nitrates, including nitroglycerin sprays and tablets for angina and the recreational drugs called poppers (amyl or butyl nitrite and nitrate), are an absolute contraindication with sildenafil. The combination can cause a dangerous drop in blood pressure.

People often assume a day later is safe. The label does not say that. It states that although levels at 24 hours are much lower than at the peak, it is unknown whether nitrates can be given safely at that point. In the higher exposure groups above, 24 hour levels are 3 to 8 times higher again. If you develop chest pain after taking sildenafil, call emergency services and tell them what you took and when.

How sildenafil compares with the other ED tablets

Drug	Half-life	Label timing
Sildenafil	About 4 hours	About 1 hour before, range 30 minutes to 4 hours
Vardenafil	About 4 to 5 hours	About 60 minutes before
Avanafil	About 5 hours	As early as about 15 minutes before (30 minutes for 50 mg)
Tadalafil	About 17.5 hours	At least 30 minutes before; effect up to 36 hours

Sildenafil, vardenafil and avanafil work over a similar window. Tadalafil is the one that changes the planning. Our tadalafil versus sildenafil comparison and generic Cialis guide cover the trade, and the avanafil guide covers the fastest onset of the four.

Getting the most from the window

• Take it about an hour before, on a light stomach. After a heavy meal, expect it to take about an hour longer.
• Do not give up at 30 minutes. The median in trials was 25 to 36 minutes, and many men take longer.
• Arousal is required. Nothing happens without stimulation, which is the most common reason a first dose seems to fail.
• If plans slip by a few hours, the tablet may still help. Do not take a second one.
• Judge it over several attempts. The trials that set the success rates ran for weeks, not one night.
• Alcohol works against you. It impairs erections independently of the tablet.

Sildenafil is sold under many names, including Viagra, Cenforce, Fildena and Kamagra. The active ingredient is the same in all of them. The timing should match only if a tablet is bioequivalent to Viagra and correctly dosed, which has not been independently shown for unapproved generics. What differs is the maker, the quality control and the price.

When to see a doctor

See a doctor if sildenafil at an adequate dose, taken correctly on several occasions, does not work or does not last long enough. See one urgently for an erection lasting more than 4 hours, sudden loss of vision in one or both eyes, sudden hearing loss, or chest pain during sex.

ED can be an early sign of heart disease or diabetes. Our erectile dysfunction page covers the causes and the full range of treatment.

Sources

• VIAGRA (sildenafil citrate) tablets, US prescribing information, sections 2, 5, 7, 8 and 12. DailyMed
• Viagra EPAR product information (EU SmPC), sections 5.1 and 5.2, including orodispersible tablets. European Medicines Agency
• Yoo H et al. Comparison of pharmacokinetic characteristics of sildenafil citrate chewable tablets and film-coated tablets in healthy male subjects. Transl Clin Pharmacol 2017;25(3):153-156. PMID 32095467.
• Marcelin-Jimenez G et al. Comparison of fasting bioavailability among 100-mg commercial, 100-mg generic, and 50-mg chewable generic sildenafil tablets. Clin Ther 2012;34(3):689-98. PMID 22386826.
• Padma-Nathan H et al. Minimal time to successful intercourse after sildenafil citrate. Urology 2003;62(3):400-3. PMID 12946731.
• Eardley I et al. Onset and duration of action of sildenafil for the treatment of erectile dysfunction. Br J Clin Pharmacol 2002;53 Suppl 1:61S-65S. PMID 11879261.
• Gingell C et al. Duration of action of sildenafil citrate in men with erectile dysfunction. J Sex Med 2004;1(2):179-84. PMID 16422972.
• Moncada I et al. Efficacy of sildenafil citrate at 12 hours after dosing: re-exploring the therapeutic window. Eur Urol 2004;46(3):357-60. PMID 15306108.
• Zinner N et al. Do food and dose timing affect the efficacy of sildenafil? J Sex Med 2007;4(1):137-44. PMID 17233779.
• Aversa A et al. Effects of sildenafil administration on seminal parameters and post-ejaculatory refractory time in normal males. Hum Reprod 2000;15(1):131-4. PMID 10611201.
• Mondaini N et al. Sildenafil does not improve sexual function in men without erectile dysfunction but does reduce the postorgasmic refractory time. Int J Impot Res 2003;15(3):225-8. PMID 12904810.
• Ekmekcioglu O et al. Effects of sildenafil citrate on ejaculation latency, detumescence time, and refractory period. Urology 2005;65(2):347-52. PMID 15708051.

This article is for information only and is not medical advice. Sildenafil is a prescription medicine. Talk to a doctor or pharmacist before starting, stopping or changing any treatment.