How Long Does Sildenafil Last? What the Label Says

Sildenafil peaks in about an hour and has a half-life of about 4 hours. Food, some medicines and kidney or liver problems change that.

Sildenafil's effect on erections typically lasts about 4 to 6 hours in common summaries, but the FDA label does not state an effect duration. What it does state is how the drug moves through the body: the highest blood level comes 30 to 120 minutes after a dose (median 60 minutes) on an empty stomach, and the terminal half-life of sildenafil and its main active metabolite is about 4 hours.¹ The label also says sildenafil has no effect without sexual stimulation, so the pill does not produce an erection by itself for as long as it remains in the blood.¹

What does the Viagra label say about how long sildenafil lasts?

The prescribing information gives timing for dosing and absorption, not a promised length of effect. The recommended dose is taken about 1 hour before sexual activity, though it may be taken anywhere from 30 minutes to 4 hours before. The maximum recommended frequency is once per day.¹ Most of the trials behind the label assessed efficacy about 60 minutes after the dose, which matches the median time to peak.¹

Many web guides turn this into "lasts 4 to 6 hours". That figure is a reasonable reading of a roughly 4 hour half-life, but it is an estimate drawn from blood levels. It is not a measured length of erection, and it is not in the label as a duration claim.

What does a 4 hour half-life actually mean?

A half-life is the time for the blood level to fall by half. After one half-life about half of the dose is left, after two about a quarter, and so on. For sildenafil that is roughly 4 hours per step.¹ The level does not drop to nothing at the 4 hour mark, and the drug is not suddenly inactive at 6 hours; the effect fades as the level falls, and how strongly any one man responds at a given hour varies.

The label shows how slowly the tail clears. It says plasma levels 24 hours after a dose are much lower than at the peak, yet it still warns that it is unknown whether nitrates can be safely taken at that point.¹ That is why the nitrate contraindication does not expire after a few hours.

How long does it take sildenafil to start working?

The peak blood level arrives 30 to 120 minutes after a dose on an empty stomach, with a median of 60 minutes.¹ Taken with a high fat meal, absorption is slower: the mean delay in reaching the peak was 60 minutes, and the mean peak level was 29% lower.¹ That is why a big dinner can push the useful window later. Our guide on sildenafil with or without food sets the meal effect beside the other approved ED pills.

What makes sildenafil last longer or shorter?

The label identifies several factors that change blood levels:

• Food. A high fat meal delays the peak by about an hour and lowers it by 29%.¹
• Strong CYP3A4 inhibitors such as ritonavir. Ritonavir raised sildenafil exposure 11-fold, and the label recommends a 25 mg dose with a maximum of 25 mg in 48 hours for men taking it.¹
• Severe kidney impairment. In men with creatinine clearance under 30 mL/min, sildenafil exposure roughly doubled, and the label suggests considering a 25 mg starting dose.¹
• Liver disease such as cirrhosis. The label lists cirrhosis among the conditions where levels are higher and a lower starting dose should be considered.¹
• Dose. The label allows adjustment between 25 mg and 100 mg based on effectiveness and tolerance.¹ Our page on sildenafil 20 mg explains why that strength belongs to a different medicine.

Alcohol, age and general health are often listed in web guides as well, but this label summary does not quantify them as duration factors, so we do not either.

How does sildenafil compare with other ED pills on duration?

So sildenafil sits with vardenafil and avanafil as a short half-life drug, and tadalafil is the long one. A half-life is not a ranking of effectiveness. For how the doses of tadalafil behave, see tadalafil 20 mg, and for what is known about taking two of these medicines, sildenafil and tadalafil together.

Does sildenafil keep an erection going for hours?

No. The label's mechanism section explains that sildenafil acts only after sexual stimulation releases nitric oxide; it then slows the breakdown of cGMP, which helps blood flow into the penis.¹ It does not hold an erection in place, and an erection normally ends for ordinary reasons. That also means a pill still in the blood is not a signal that sex has to happen.

When is a long erection an emergency?

Rarely, a PDE5 inhibitor is followed by a prolonged erection. The Viagra label reports prolonged erections of more than 4 hours and priapism (painful erections lasting more than 6 hours) infrequently since approval, and warns that untreated priapism can lead to tissue damage and permanent loss of potency.¹ The tadalafil, vardenafil and avanafil labels carry the same warning, and each says to seek emergency treatment if an erection lasts more than 4 hours.²³⁴ This is the one duration number to remember.

Sudden loss of vision or hearing is the other reason to stop and seek care. The Viagra label tells patients to stop the drug and seek prompt medical attention in the event of sudden decrease or loss of hearing.¹

Questions to bring to a clinician

If a dose seems to fade too early or last too long, the useful questions are about the person, not a calendar: what medicines are on the list, whether liver or kidney problems apply, how meals and timing fit the plan, and whether a different drug or schedule suits the situation better. A clinician can adjust the dose within the label range or consider another drug. Do not repeat a dose within the same day: the label's maximum is once a day.¹ The ED medication interactions page lists the combinations that change those answers.

Questions readers ask

How long does sildenafil stay in the body?

The label gives a terminal half-life of about 4 hours for sildenafil and its main metabolite. Levels 24 hours after a dose are much lower than the peak, but the label says it is unknown whether nitrates can be safely taken then.

How long does it take sildenafil to start working?

Peak blood levels occur 30 to 120 minutes after a dose on an empty stomach, with a median of 60 minutes. A high fat meal delays the peak by about 60 minutes on average.

Will sildenafil give an erection for the whole time it is in my system?

No. The label says sildenafil has no effect without sexual stimulation. It helps blood flow when stimulation releases nitric oxide.

Can I take a second sildenafil dose if the first wears off?

The label's maximum recommended frequency is once per day. Ask a clinician before changing the dose or timing.

What should I do if an erection lasts more than 4 hours?

Seek emergency medical care. The label warns that untreated priapism can damage penile tissue and cause permanent loss of potency.

Further reading

Part of our guide: How ED Medications Work: Timing, Food, Interactions and Combinations

• Sildenafil Headache: How Common Is It?
• Tadalafil With Alcohol: How Much Is Too Much?
• What Is Tadalafil Used For? The Three Approved Uses
• Tadalafil Brand Names: Which Brand Is Used for What