Sildenafil is a widely prescribed treatment for erectile dysfunction in the UK, available on NHS prescription or as Viagra Connect from pharmacies. Many men wonder how long an erection will last after taking this medication. Understanding the duration of sildenafil's effects—and the difference between the drug's active window and the length of an individual erection—is essential for safe, effective use. This article explains how sildenafil works, how long its effects typically last, factors that influence duration, and important safety considerations including when to seek urgent medical help.

How Sildenafil Works to Produce an Erection

Sildenafil belongs to a class of medicines called phosphodiesterase type 5 (PDE5) inhibitors. It works by enhancing the natural erectile response to sexual stimulation rather than causing an erection directly. When a man becomes sexually aroused, nerve signals trigger the release of nitric oxide in the erectile tissue of the penis. This chemical messenger activates an enzyme that produces cyclic guanosine monophosphate (cGMP), which relaxes the smooth muscle in the blood vessels of the penis, allowing increased blood flow.

Under normal circumstances, another enzyme called PDE5 breaks down cGMP, which eventually causes the erection to subside. Sildenafil inhibits PDE5 , thereby preventing the breakdown of cGMP and allowing it to accumulate. This results in prolonged smooth muscle relaxation and sustained blood flow to the penis, making it easier to achieve and maintain an erection when sexually stimulated.

It is important to understand that sildenafil does not cause spontaneous erections. Sexual stimulation is still required for the medication to be effective. The drug simply enhances the body's natural erectile mechanism by improving blood flow. Sildenafil is generally available on NHS prescription in the UK for erectile dysfunction, or can be purchased as Viagra Connect (50mg) from pharmacies following assessment by a pharmacist. The medication typically begins to work within 30 to 60 minutes of taking it, though this can vary between individuals depending on factors such as food intake and individual metabolism.

Importantly, sildenafil must not be taken by people using nitrate medications (including GTN spray or tablets and nicorandil) or the medicine riociguat, as this combination can cause a dangerous drop in blood pressure. Sexual activity may also be inadvisable in some cardiovascular conditions.

Expected Duration of Erection with Sildenafil

When discussing how long an erection lasts with sildenafil, it is essential to distinguish between the duration of the drug's effect and the duration of an individual erection. Sildenafil remains active in the body for around four hours after taking a standard dose (typically 50mg, though doses range from 25mg to 100mg). During this window, the medication facilitates the ability to achieve an erection when sexually aroused, but it does not mean a continuous erection throughout this period.

An individual erection achieved whilst sildenafil is active typically lasts for the duration of sexual activity, usually subsiding naturally after ejaculation or when sexual stimulation ceases. This is the normal physiological response and mirrors what would occur without medication, though the erection may be firmer and easier to maintain. Most men find that they can achieve multiple erections during the four-hour effective window if sexual stimulation occurs again.

The half-life of sildenafil is approximately three to five hours, meaning that after this time, half of the drug has been metabolised and eliminated from the body. However, some effect may persist beyond this as the remaining medication continues to work, though with diminishing effectiveness. Individual responses vary considerably based on factors such as age, overall health, liver and kidney function, and concurrent medications. It is worth noting that sildenafil does not affect sexual desire or libido—it only assists with the physical mechanism of achieving an erection. If you find the medication is not working as expected, or if erections are not lasting long enough for satisfactory sexual activity, consult your GP or prescriber, as dose adjustment may be appropriate.

Factors That Affect How Long Sildenafil Lasts

Several factors can influence both the onset and duration of sildenafil's effects. Understanding these can help optimise treatment outcomes:

Food intake: Taking sildenafil with a large or high-fat meal can significantly delay absorption, meaning the medication takes longer to work and may have reduced effectiveness. For best results, take sildenafil on an empty stomach or after a light meal.

Alcohol consumption: Whilst moderate alcohol intake is unlikely to interfere significantly with sildenafil, excessive drinking can impair erectile function independently and may reduce the medication's effectiveness. Alcohol is also a vasodilator, which can compound the blood-pressure-lowering effects of sildenafil.

Age and metabolism: Older men typically metabolise sildenafil more slowly, which may result in prolonged effects. Men over 65 often start on lower doses (25mg) for this reason. Conversely, younger men with faster metabolism may find the effects wear off more quickly.

Liver and kidney function: Sildenafil is metabolised primarily in the liver and excreted via the kidneys. Impaired function in either organ can lead to higher drug levels in the bloodstream and prolonged effects. A lower starting dose (25mg) is often recommended for men with hepatic or renal impairment.

Other medications: Certain drugs can interact with sildenafil, affecting how long it lasts:

• Nitrates and nicorandil are strictly contraindicated as they can cause dangerous drops in blood pressure

• Riociguat is contraindicated due to risk of hypotension

• Alpha-blockers (used for prostate problems or high blood pressure) may cause symptomatic hypotension; a lower starting dose (25mg) and separation of dosing times is recommended

• CYP3A4 inhibitors (such as erythromycin, ketoconazole, and some HIV protease inhibitors) can increase sildenafil levels and prolong its effects

• Grapefruit juice can inhibit metabolism, potentially increasing sildenafil levels

Underlying health conditions: Cardiovascular disease, diabetes, and neurological conditions can all affect erectile function and may influence response to sildenafil. Psychological factors such as anxiety or stress can also impact treatment success, even when the medication is working physiologically.

What to Do If Your Erection Lasts Too Long

Whilst sildenafil helps men achieve erections suitable for sexual activity, a prolonged erection lasting more than four hours—known as priapism—is a medical emergency requiring immediate attention. Priapism is rare with sildenafil but can occur, particularly if the medication is taken in excessive doses, combined with other erectile dysfunction treatments, or in men with certain predisposing conditions such as sickle cell disease, leukaemia, or multiple myeloma.

There are two types of priapism: ischaemic (low-flow) and non-ischaemic (high-flow). Ischaemic priapism is the more serious form, where blood becomes trapped in the penis and cannot drain away. This deprives the erectile tissue of oxygen, and if left untreated for several hours, can result in permanent damage to the erectile tissue and long-term erectile dysfunction. Non-ischaemic priapism, caused by excessive arterial blood flow, is less common and generally less harmful, but still requires medical assessment.

If you experience an erection lasting longer than four hours, you should:

• Seek immediate medical attention by attending your nearest Accident & Emergency department

• Call 999 if you cannot get to A&E promptly or feel very unwell

• Do not wait to see if it resolves on its own—early treatment significantly improves outcomes

• Inform medical staff that you have taken sildenafil and provide details of the dose and timing

Treatment for priapism may include aspiration of blood from the penis, injection of medications to constrict blood vessels, or in rare cases, surgical intervention. To reduce the risk of priapism, never exceed the prescribed dose of sildenafil, avoid combining it with other erectile dysfunction treatments without medical advice, and inform your doctor of any blood disorders or anatomical abnormalities of the penis.

Getting the Most from Sildenafil Treatment

To optimise your response to sildenafil and ensure safe, effective use, consider the following evidence-based recommendations:

Timing and planning: Take sildenafil approximately one hour before anticipated sexual activity. Whilst it may work within 30 minutes for some men, allowing a full hour ensures optimal absorption and effect. Remember that sexual stimulation is required—the tablet alone will not produce an erection.

Dosing guidance: The usual starting dose is 50mg, taken as needed, with a maximum of one dose in 24 hours. Your doctor may adjust this to 25mg if you experience side effects, or increase to 100mg if the response is inadequate. Never take more than the prescribed dose, as this increases the risk of adverse effects without necessarily improving efficacy.

Safety precautions:

• Never take sildenafil with nitrate medications (such as GTN spray/tablets or nicorandil) or riociguat

• If you experience chest pain after taking sildenafil, seek urgent medical help and tell healthcare providers you've taken sildenafil—do not take nitrates for at least 24 hours

• If taking alpha-blockers for prostate problems or blood pressure, discuss timing with your doctor as dose separation may be needed

Lifestyle modifications: Addressing underlying risk factors for erectile dysfunction can enhance treatment outcomes. These include:

• Maintaining a healthy weight and regular physical activity

• Stopping smoking, which damages blood vessels

• Limiting alcohol consumption

• Managing stress and anxiety, potentially with psychological support

• Optimising control of conditions such as diabetes, hypertension, and high cholesterol

Managing side effects: Common adverse effects of sildenafil include headache, facial flushing, indigestion, and nasal congestion. These are usually mild and transient. Taking the medication with water and avoiding large meals can help reduce gastrointestinal symptoms. Seek urgent medical attention if you experience:

• Sudden vision loss in one or both eyes

• Sudden hearing loss or ringing in the ears

• Severe dizziness or fainting

• Chest pain or irregular heartbeat

• Allergic reaction (rash, itching, swelling, severe dizziness)

You can report any suspected side effects to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk.

When to seek further help: If sildenafil is not effective after trying it on at least eight separate occasions, contact your GP. There may be underlying causes of erectile dysfunction that require investigation, or alternative treatments may be more suitable. NICE guidance recommends considering referral to specialist services if first-line oral treatments fail, or if there are complex underlying causes requiring further assessment.

Frequently Asked Questions