Sildenafil side effects: A complete guide

DoktorABC editorial team

Accurate, up-to-date health information written by our editorial team and reviewed by UK-registered prescribers.

Why sildenafil causes side effects

Understanding why side effects happen makes them easier to manage. Sildenafil belongs to a class of medicines called PDE5 inhibitors. It works by widening blood vessels which enables an increased blood flow to the penis during sexual arousal, supporting the ability to get and maintain an erection.

The same mechanism that makes sildenafil effective for erectile dysfunction also affects blood vessels elsewhere in the body. This widening of blood vessels, known as vasodilation, is the direct cause of most of sildenafil's common side effects: headaches, flushing, a stuffy nose, and dizziness are all the result of increased blood flow in areas beyond the intended target.

The most common side effects of sildenafil

The following side effects are classified as very common or common based on EMA product information and clinical trial data. They affect a meaningful proportion of men who take sildenafil, are generally mild to moderate in severity, and typically resolve within a few hours.

The most common side effects reported in clinical trials include headache, flushing, indigestion, nasal congestion, back pain, muscle aches, nausea, dizziness, abnormal vision and rash. 

Headache

The most frequently reported side effect of sildenafil is a headache. It occurs because vasodilation increases blood flow to the head. It typically comes on within an hour of taking the tablet and resolves within a few hours. Staying well hydrated before and after taking sildenafil can help reduce its severity.

Flushing

A warm, reddening sensation in the face, neck, or chest is common and is again a direct result of increased blood flow. It is harmless and usually passes within one to two hours. Some men find it more pronounced when sildenafil is taken with alcohol or a hot drink.

Indigestion and nausea

Sildenafil can relax the muscular valve between the stomach and the oesophagus, which may cause acid to rise, leading to heartburn or an unsettled stomach. Taking sildenafil with or after a light meal can help, though a heavy or high-fat meal may delay how quickly it takes effect.

Nasal congestion

A blocked or runny nose is a common and generally minor side effect caused by vasodilation in the nasal passages. It usually clears as the medication wears off.

Dizziness

Mild dizziness can occur as a result of a modest drop in blood pressure following vasodilation. It is more likely in men who are also taking antihypertensive medication. As dizziness and altered vision were reported in clinical trials with sildenafil, patients should be aware of how they react before driving or operating machinery.

Less common but notable side effects

There are additional side effects that occur in a smaller proportion of men and are generally mild, but they are worth being aware of.

Back pain and muscle aches

With administration more frequently than once a day, there was an increased frequency of muscle aches, which was transient and without evidence of muscular damage. When taken at the recommended frequency of once per day at most, muscle aches are uncommon and typically mild. 

Visual disturbances

Sildenafil has shown associations with changes in colour vision, alterations in light perception, and hazy vision. This occurs because PDE5 is also present in the retina of the eye, and sildenafil can mildly inhibit its activity there. The most commonly reported visual change is a blue-green tinge to vision, which is temporary and resolves as the medication clears the system. It is more likely at higher doses.

Blurred vision

Mild blurring of vision is classified as uncommon and is again temporary. If blurred vision is persistent or worsens, contact your prescriber.

Serious side effects requiring immediate medical attention

The following side effects are rare, but they are serious. If you experience any of them, stop taking sildenafil and seek emergency medical help immediately.

Priapism

A prolonged erection lasting more than four hours, known as priapism, is a medical emergency. Without prompt treatment it can cause permanent damage to the erectile tissue. If you have an erection that has lasted longer than four hours, seek emergency medical help immediately regardless of whether it is painful.

Sudden loss of vision

Rare cases of non-arteritic anterior ischaemic optic neuropathy (NAION) have been reported in men taking PDE5 inhibitors, including sildenafil. This presents as a sudden partial or complete loss of vision in one eye. It is rare and a causal link has not been definitively established, but any sudden change in vision while taking sildenafil requires immediate medical assessment.

Sudden hearing loss

Rarely, sildenafil has shown correlations with hearing loss that, in some cases, is reversible. Sudden decrease or loss of hearing, sometimes accompanied by ringing in the ears or dizziness, has been reported in post-marketing data. Stop taking sildenafil and seek medical help immediately if this occurs. 

Severe drop in blood pressure

Sildenafil can cause a significant and potentially dangerous drop in blood pressure when taken with nitrates (medicines used for chest pain such as glyceryl trinitrate). This combination is absolutely contraindicated. Severe hypotension can cause fainting, collapse, and in serious cases, cardiovascular events.

Severe allergic reaction

Signs include swelling of the face, lips, tongue, or throat, difficulty breathing, and severe skin reactions. This is rare but requires emergency medical attention.

Side effects in specific groups

The experience of side effects can vary depending on your health background. Here is what the evidence shows for three commonly relevant groups.

Older men

Sildenafil is cleared from the body more slowly in older men, meaning blood levels remain higher for longer. This can increase both the effectiveness and the potential for side effects. Starting at a lower dose (25 mg rather than 50 mg) is often recommended for men over 65. Discuss the right starting dose with your prescriber.

Men with cardiovascular conditions

Sexual activity itself increases heart rate and blood pressure, and this is an important consideration for men with existing heart conditions. Sildenafil is contraindicated alongside nitrate medicines. Men with a history of heart attack, stroke, or significant cardiovascular disease should discuss whether sildenafil is appropriate for them before starting. The modest blood pressure reduction caused by sildenafil is generally well tolerated, but can be more pronounced in men already taking antihypertensive medicines.

Men with diabetes

Men with diabetes are more likely to have a concurrent cardiovascular condition and may be taking a range of other medicines, making a thorough medical review before starting sildenafil particularly important. Sildenafil is generally effective and well tolerated in men with diabetes, but the interaction profile with other medications warrants careful prescriber assessment.

How long do sildenafil side effects last?

Most side effects of sildenafil are short-lived, typically resolving within two to six hours as the medication clears from the body. Sildenafil has a half-life of approximately three to five hours, meaning blood levels drop significantly over that period.

Several factors influence how pronounced side effects are and how long they last:

• Dose: Higher doses produce more pronounced side effects. Doses of 200 mg did not result in increased efficacy but the incidence of adverse reactions including headache, flushing, dizziness, and indigestion increased. Taking the lowest effective dose minimises the chance of side effects.
• Food: Taking sildenafil with a large, high-fat meal delays absorption and can extend the duration of both its effects and associated side effects.
• Alcohol: Alcohol adds to the blood pressure-lowering effect of sildenafil and can worsen flushing, dizziness, and headache. Drinking heavily before taking sildenafil is not recommended.
• Age: As noted above, older men clear sildenafil more slowly, which can extend both effects and side effects.

Tips for minimising sildenafil side effects

Most side effects can be reduced with a few straightforward adjustments.

• Take sildenafil on an empty stomach or after a light meal rather than a heavy one
• Stay well hydrated before and after taking the tablet, which can reduce headache severity
• Avoid alcohol, or keep it to a minimum, on the same occasion as taking sildenafil
• Start at the lowest effective dose (25 mg or 50 mg) and only increase if needed, under prescriber guidance
• Avoid taking sildenafil more than once in 24 hours
• Allow yourself time to rest after taking sildenafil if dizziness is an issue, particularly in the first few times you use it

If a specific side effect is persistent or affecting your quality of life, speak to your prescriber. A dose adjustment, a different formulation, or an alternative PDE5 inhibitor such as tadalafil may suit you better.

When to contact a doctor or stop taking sildenafil

Contact your prescriber if:

• Side effects are persistent, worsening, or significantly affecting your daily life
• You experience any visual changes beyond the mild temporary tinge described above
• You have an erection lasting more than two hours
• You feel chest pain, shortness of breath, or palpitations during or after sexual activity
• You are unsure whether sildenafil interacts with another medicine you are taking

Stop taking sildenafil and seek emergency help if you experience:

• A prolonged erection lasting more than four hours
• Sudden loss or significant change in vision
• Sudden loss of hearing
• Signs of a severe allergic reaction
• Severe chest pain or a feeling of collapse

Report any suspected side effects to the MHRA via the Yellow Card scheme

Sildenafil vs other ED medications: a brief note

Sildenafil, tadalafil, and vardenafil all belong to the same class of medicines and share a broadly similar side effect profile. Treatment-related adverse events with PDE5 inhibitors are generally mild to moderate, showing minor differences across the class. Headache, facial flushing, nasal congestion, and indigestion are the most common adverse events across all of them. 

The main practical differences are in duration and timing. Tadalafil lasts significantly longer (up to 36 hours) and is also available as a daily low dose, which some men find produces fewer noticeable side effects by maintaining a steady blood level rather than a peak.

Final thoughts

Sildenafil is a well-established, extensively studied treatment for erectile dysfunction, and the large majority of men who take it at the recommended dose experience only mild, manageable side effects that resolve within a few hours. Knowing what to expect, and knowing the difference between a common, temporary reaction and a symptom that requires urgent attention, puts you in a much better position to use it safely and confidently.

If you have questions about whether sildenafil is right for you, or if you are experiencing side effects that concern you, a UK-registered prescriber can review your health history and advise accordingly. DoktorABC connects UK patients with licensed prescribers and GPhC-registered pharmacies for private ED treatment, with clinical support throughout.

FAQ

The DoktorABC medical advisory board

Dr. Roland Ruiken

Medical advisor, Norway

Dr. Viktor Simunovic

Medical advisor, Croatia

To the medical advisory board