Sildenafil is a prescription medication widely used to treat erectile dysfunction (ED) in men. As a phosphodiesterase type 5 (PDE5) inhibitor, it enhances the body's natural erectile response by improving blood flow to the penis during sexual arousal. Sildenafil works by blocking an enzyme that breaks down a chemical messenger responsible for relaxing blood vessels, making it easier to achieve and maintain an erection. Sexual stimulation is still required for the medication to be effective. Available in various strengths, sildenafil typically begins working within 30 to 60 minutes and can help restore sexual function, confidence, and relationship satisfaction for many men experiencing ED.

What Does Sildenafil Do to a Man

Sildenafil is a prescription medication primarily used to treat erectile dysfunction (ED) in men. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors, which work by enhancing the natural erectile response to sexual stimulation. When a man is sexually aroused, the body releases nitric oxide in the erectile tissue of the penis, which activates an enzyme that produces cyclic guanosine monophosphate (cGMP). This chemical messenger relaxes the smooth muscle cells in the blood vessels of the penis, allowing increased blood flow into the corpora cavernosa—the spongy tissue that becomes engorged during an erection.

Sildenafil works by inhibiting the PDE5 enzyme , which normally breaks down cGMP. By blocking this enzyme, sildenafil allows cGMP levels to remain elevated for longer, promoting sustained relaxation of blood vessels and improved blood flow to the penis. This makes it easier for men with ED to achieve and maintain an erection sufficient for sexual activity. It is important to note that sildenafil does not cause spontaneous erections—sexual stimulation is still required for the medication to be effective.

The medication typically begins to work within 30 to 60 minutes of taking it orally, with effects lasting for approximately four to five hours. Taking sildenafil on an empty stomach improves absorption; a heavy or fatty meal can delay onset and reduce effectiveness. Sildenafil is also licensed under different brand names for treating pulmonary arterial hypertension (PAH), a condition affecting blood pressure in the lungs. PAH formulations are not interchangeable with ED products without specialist advice. In the UK, sildenafil for ED is available on prescription from a GP or through regulated online pharmacy services. Additionally, sildenafil 50 mg (Viagra Connect) is available as a pharmacy medicine for men aged 18 and over following a consultation with a pharmacist.

Effects and Benefits of Taking Sildenafil

The primary benefit of sildenafil for men with erectile dysfunction is the restoration of erectile function, which can significantly improve quality of life, intimate relationships, and psychological wellbeing. Clinical trials have demonstrated that sildenafil is effective in approximately 60–70% of men with ED overall, though effectiveness varies by cause. Men with ED related to diabetes, after prostate surgery, or with severe cardiovascular disease typically show lower response rates than those with primarily psychological causes.

Beyond the physical effects, sildenafil can have important psychological and emotional benefits. Erectile dysfunction often leads to anxiety, reduced self-esteem, relationship difficulties, and avoidance of intimacy. By successfully treating the physical symptoms, sildenafil can help break this cycle, reducing performance anxiety and restoring confidence. Many men report improved relationship satisfaction and reduced stress related to sexual performance after starting treatment.

Sildenafil is generally well-tolerated and offers flexibility in dosing. In the UK, it is available in 25 mg, 50 mg, and 100 mg tablets, allowing healthcare providers to tailor the dose to individual needs and tolerability. The standard starting dose is typically 50 mg, taken approximately one hour before sexual activity. A lower starting dose of 25 mg is recommended for men aged 65 and over, those with hepatic or severe renal impairment, and those taking certain medications that inhibit CYP3A4 enzymes (such as erythromycin, ketoconazole or ritonavir). The dose may be increased to 100 mg or decreased to 25 mg based on effectiveness and side effects. Men are usually advised not to take sildenafil more than once in a 24-hour period. Excessive alcohol consumption may reduce erectile response and increase side effects such as dizziness.

It is worth noting that whilst sildenafil treats the symptoms of ED, it does not address underlying causes. The NICE guidelines recommend that men with ED should receive a comprehensive assessment to identify and manage any underlying health conditions, such as cardiovascular disease, diabetes, or hormonal imbalances, which may be contributing to erectile problems.

Common Side Effects Men May Experience

Like all medications, sildenafil can cause side effects, although not everyone experiences them. The most commonly reported side effects are generally mild to moderate and tend to diminish with continued use. These include:

• Headaches – the most frequent side effect, occurring in approximately 10–15% of users, caused by the vasodilatory effects of the medication

• Facial flushing – a sensation of warmth and redness in the face and neck

• Indigestion or dyspepsia – stomach discomfort or acid reflux

• Nasal congestion – a blocked or stuffy nose

• Dizziness – particularly when standing up quickly, due to temporary blood pressure changes

Some men may experience visual disturbances, such as a blue tinge to vision, increased sensitivity to light, or blurred vision. These effects are usually mild and transient, resolving within a few hours. They occur because sildenafil can have a mild effect on PDE6, an enzyme found in the retina. Seek urgent medical care if you experience sudden decrease or loss of vision.

More serious side effects are rare but require immediate medical attention. These include:

• Priapism – a painful erection lasting more than four hours, which is a medical emergency requiring urgent treatment to prevent permanent damage

• Sudden vision loss – which may indicate non-arteritic anterior ischaemic optic neuropathy (NAION)

• Sudden hearing loss or tinnitus – ringing in the ears

• Chest pain or irregular heartbeat – particularly during or after sexual activity

If chest pain occurs during or after sexual activity, stop immediately, call 999, and do not take nitrate medications. Inform healthcare professionals that you have taken sildenafil. Men experiencing severe side effects or symptoms suggestive of an allergic reaction (such as difficulty breathing, swelling of the face or throat, or severe skin rash) should seek emergency medical help immediately. Report any suspected side effects to your doctor or pharmacist, or via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Who Should Not Take Sildenafil

Sildenafil is not suitable for all men, and there are several important contraindications and precautions to consider. The absolute contraindications include the concurrent use of nitrate medications or nitric oxide donors, which are commonly prescribed for angina (chest pain). These include glyceryl trinitrate (GTN), isosorbide mononitrate, and isosorbide dinitrate. The combination of sildenafil and nitrates can cause a dangerous drop in blood pressure, potentially leading to cardiovascular collapse. This contraindication also extends to recreational drugs containing nitrates, such as amyl nitrite ('poppers'). Sildenafil is also contraindicated with riociguat, a medication used for pulmonary hypertension.

Men with certain cardiovascular conditions should not take sildenafil or should only do so under close medical supervision. These include:

• Recent heart attack or stroke (within the last six months)

• Unstable angina or angina occurring during sexual intercourse

• Severe heart failure

• Uncontrolled high blood pressure (hypertension) or very low blood pressure (hypotension)

• Significant heart rhythm abnormalities

Sildenafil should be used with caution in men with severe liver impairment or severe kidney disease, where a starting dose of 25 mg should be considered. Men with certain eye conditions such as retinitis pigmentosa should discuss the risks carefully with their doctor, as sildenafil is not recommended in these cases. Men with a history of priapism or conditions that predispose to priapism (such as sickle cell anaemia, multiple myeloma, or leukaemia) should also discuss the risks carefully with their doctor.

Certain medications can interact with sildenafil. Men taking alpha-blockers for prostate problems or high blood pressure should ensure they are stable on this therapy before starting sildenafil, and should begin with a 25 mg dose to reduce the risk of postural hypotension. Strong CYP3A4 inhibitors (including some antibiotics, antifungals, and HIV protease inhibitors) increase sildenafil levels; a 25 mg starting dose should be considered and high doses avoided. It is essential to inform your GP or pharmacist about all medications, supplements, and herbal remedies you are taking.

Before prescribing sildenafil, healthcare professionals should conduct a thorough assessment including medical history, current medications, and cardiovascular risk factors. Men who have not been sexually active or who have concerns about their fitness for sexual activity should discuss this with their GP, as sexual activity itself carries cardiovascular demands that may not be appropriate for all individuals.

Frequently Asked Questions