Sildenafil Overdose Symptoms: Signs & What to Do

Sildenafil Overdose Symptoms: What You Need to Know

Published: 7 November 2026

Sildenafil overdose symptoms can include severe headache, dizziness, flushing, visual disturbances (such as blurred vision or a blue tinge), prolonged erection (priapism), fainting, and dangerously low blood pressure. Taking more than the prescribed dose of sildenafil (Viagra) increases the risk of these effects and can be harmful. If you suspect an overdose, seek medical help immediately by calling 111 or attending A&E. This page explains how to recognise overdose symptoms, what to do if you take too much, and how to use sildenafil safely.

What Are the Main Sildenafil Overdose Symptoms?

The most common sildenafil overdose symptoms include severe headache, dizziness, flushing (redness and warmth in the face or chest), visual changes (blurred vision, increased sensitivity to light, or a blue tinge to vision), and nausea [3]. These effects occur because sildenafil works by relaxing blood vessels, and too much of the medicine can cause excessive blood vessel widening throughout the body.

More serious overdose symptoms include a dangerous drop in blood pressure, which can lead to fainting, confusion, or loss of consciousness. An erection lasting more than four hours (priapism) is a medical emergency that requires immediate treatment to prevent permanent damage to the penis [3]. Some people may also experience chest pain, irregular heartbeat, or difficulty breathing after taking too much sildenafil.

Visual disturbances are particularly important to watch for. In rare cases, sildenafil overdose has been associated with sudden vision loss in one or both eyes, a condition called non-arteritic anterior ischaemic optic neuropathy (NAION) [3]. If you experience any sudden changes in vision or hearing, stop taking sildenafil and seek urgent medical attention. The severity of symptoms generally increases with the amount taken above the recommended dose.

How Quickly Do Overdose Symptoms Appear?

Sildenafil is absorbed relatively quickly, with peak blood levels typically reached within 30 to 120 minutes after taking a tablet [3]. This means overdose symptoms usually begin within one to two hours of taking too much sildenafil. However, because the medicine remains active in your body for several hours, symptoms can persist or worsen over time. The effects of sildenafil typically last for four to five hours, though some effects on blood vessels can continue for longer. If you have taken more than the prescribed dose, monitor yourself closely during this period and do not hesitate to seek medical help if symptoms develop or worsen.

What Is the Maximum Safe Dose of Sildenafil?

The maximum recommended dose of sildenafil for erectile dysfunction is 100mg taken once in a 24-hour period [3]. Most men start on 50mg, which can be adjusted up to 100mg or down to 25mg depending on effectiveness and side effects. Taking more than 100mg in a day significantly increases the risk of side effects without improving effectiveness. Sildenafil is not designed to work better at higher doses; it either helps achieve an erection with sexual stimulation or it does not.

Some men mistakenly believe that taking a double dose will produce stronger or longer-lasting results, but this is not how sildenafil works [3]. The medicine requires sexual arousal to be effective, and exceeding the recommended dose simply exposes you to greater risk of harm. If 100mg is not effective for you, speak to your prescriber about alternative treatments or investigating underlying causes of erectile dysfunction, rather than increasing the dose on your own.

It is also crucial never to take sildenafil more than once a day, even if the first dose did not work as expected. Your body needs time to clear the medicine, and taking a second dose too soon can lead to dangerous accumulation in your bloodstream. If you have kidney or liver problems, your prescriber may recommend a lower maximum dose, as these conditions can slow down how your body processes sildenafil [3].

What Should You Do If You Take Too Much Sildenafil?

If you have taken more sildenafil than prescribed, contact NHS 111 immediately for advice, or attend your nearest A&E department if you are experiencing severe symptoms such as fainting, chest pain, difficulty breathing, or an erection lasting more than four hours [3]. Do not wait to see if symptoms develop; early medical assessment is important. When you contact medical services, tell them exactly how much sildenafil you took and when, along with any other medicines you are taking.

While waiting for medical help, sit or lie down to reduce the risk of fainting from low blood pressure. Do not drive yourself to hospital if you feel dizzy or unwell. Avoid taking any other medicines, including over-the-counter painkillers, without medical advice, as they could interact with the sildenafil in your system. Do not try to make yourself vomit unless specifically instructed to do so by a healthcare professional.

If someone else has taken sildenafil accidentally (for example, a child or someone for whom it was not prescribed), seek emergency medical attention immediately by calling 999 or going to A&E, even if they seem well. Sildenafil can cause serious harm in people who should not take it, particularly those on certain heart medicines. Keep the medicine packet or information leaflet with you to show medical staff. Treatment for sildenafil overdose is supportive and focuses on managing symptoms, particularly blood pressure and heart rate [3].

Can Sildenafil Overdose Be Fatal?

Sildenafil overdose is rarely fatal in otherwise healthy individuals, but it can be life-threatening in certain circumstances, particularly if taken with medicines that interact dangerously with it [3]. The greatest risk comes from combining sildenafil with nitrates (such as GTN spray for angina), nicorandil, or recreational drugs called 'poppers' (alkyl nitrites). This combination can cause a catastrophic drop in blood pressure that can be fatal. Very high doses of sildenafil alone can also cause severe low blood pressure, heart problems, or priapism leading to permanent erectile dysfunction. This is why it is essential to follow prescribed doses and never share your medicine with others.

How Can You Avoid Sildenafil Overdose Symptoms?

The best way to avoid sildenafil overdose symptoms is to take exactly the dose prescribed by your doctor or prescriber, and never more than once in 24 hours [3]. Do not increase your dose without medical advice, even if you feel the medicine is not working as well as you hoped. If sildenafil is not effective at the prescribed dose, this may indicate that a different treatment approach is needed, or that underlying health issues need to be addressed.

Always tell your prescriber about all medicines you are taking, including over-the-counter medicines, herbal supplements, and recreational drugs. Some medicines can increase sildenafil levels in your blood (such as certain antibiotics, antifungals, and HIV medicines), meaning even a normal dose could have stronger effects [3]. Your prescriber can adjust your sildenafil dose accordingly or recommend an alternative treatment if interactions are a concern.

Store sildenafil safely out of reach of children and other household members. Never share your prescription with friends or partners, even if they have similar symptoms. What is safe for you may be dangerous for someone else, particularly if they have heart conditions or take medicines that interact with sildenafil. If you are using sildenafil obtained from Cured Pharmacy, it will be supplied following an online consultation reviewed by a UK prescriber, ensuring the dose is appropriate for your individual circumstances. Keep track of when you take your dose to avoid accidentally taking a second tablet too soon.

What Are the Common Side Effects at Normal Sildenafil Doses?

Even at the correct prescribed dose, sildenafil commonly causes mild to moderate side effects in some men. The most frequent include headache, flushing, indigestion, nasal congestion, and dizziness [3]. These effects occur because sildenafil relaxes blood vessels throughout the body, not just in the penis. Most side effects are mild and temporary, typically lasting a few hours as the medicine wears off.

Visual disturbances can occur at normal doses, including a blue tinge to vision, increased brightness, or blurred vision. These effects are usually mild and resolve on their own [3]. However, if you experience sudden vision loss in one or both eyes, stop taking sildenafil immediately and seek urgent medical attention, as this could indicate a serious condition called NAION. Similarly, sudden hearing loss or ringing in the ears (tinnitus) requires immediate medical assessment.

Less common side effects include nosebleeds, nausea, vomiting, muscle aches, and back pain. Some men experience dizziness or light-headedness, particularly when standing up quickly, due to the blood-pressure-lowering effect of sildenafil [3]. If side effects are troublesome or persistent, speak to your prescriber about adjusting your dose or trying a different erectile dysfunction treatment. Do not simply take more sildenafil in the hope that benefits will outweigh side effects; this increases your risk of harm without improving outcomes.

When Should You Seek Medical Help for Side Effects?

Seek immediate medical help (call 999 or go to A&E) if you experience chest pain during or after sex, an erection lasting more than four hours, sudden loss of vision or hearing, severe dizziness or fainting, or an allergic reaction (swelling of the face, lips, tongue or throat, difficulty breathing, or severe skin rash) [3]. These are rare but serious side effects that require urgent treatment. For less severe but persistent side effects, contact your GP or the prescriber who issued your sildenafil prescription for advice. They can review your treatment and suggest alternatives if needed.

Who Should Not Take Sildenafil and Why?

Sildenafil is not suitable for everyone, and taking it when you should not can lead to serious harm, even at normal doses. You must not take sildenafil if you are using nitrate medicines for angina or chest pain (such as glyceryl trinitrate spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, or riociguat [3]. The combination can cause a dangerous, potentially fatal drop in blood pressure. This also applies to recreational drugs called 'poppers' (alkyl or amyl nitrites), which are sometimes used during sex.

Sildenafil is also not suitable if you have recently had a heart attack or stroke, have severe heart failure, very low blood pressure, or certain inherited eye conditions affecting the retina [3]. Men with a history of priapism (prolonged erections) or conditions that increase the risk of priapism (such as sickle cell anaemia, leukaemia, or multiple myeloma) need specialist assessment before using sildenafil. If you have severe kidney or liver disease, your dose may need to be adjusted, or sildenafil may not be appropriate.

During an online consultation with Cured Pharmacy, a UK prescriber reviews your medical history, current medicines, and health conditions to ensure sildenafil is safe for you. This is why it is essential to answer all questions honestly and completely. If sildenafil is not suitable, the prescriber can recommend alternative treatments for erectile dysfunction. Never buy sildenafil from unregulated sources, as you will not receive this important safety check, and the medicine may be counterfeit or contaminated [1][2].

Can You Take Sildenafil with Other Medicines?

Sildenafil can interact with several other medicines. Alpha-blockers (such as doxazosin or tamsulosin, used for prostate problems or high blood pressure) can add to the blood-pressure-lowering effect of sildenafil, causing dizziness or fainting [3]. If you take an alpha-blocker, you should be stable on it before starting sildenafil, and your prescriber will usually recommend starting with the lowest sildenafil dose. Some medicines that affect liver enzymes (such as ritonavir, ketoconazole, itraconazole, or clarithromycin) can increase sildenafil levels in your blood, requiring dose adjustment [3]. Always tell your prescriber about every medicine you take, including over-the-counter and herbal products, so they can check for interactions.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 7 November 2026]
2. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 7 November 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 7 November 2026]

Information on this page is for educational purposes only and is not medical advice. Prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting or changing any medication.