Taking too much sildenafil can lead to serious health complications requiring urgent medical attention. Sildenafil, a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK for erectile dysfunction and pulmonary arterial hypertension, is generally safe at prescribed doses of 25 mg, 50 mg, or 100 mg. However, exceeding the recommended maximum of 100 mg in 24 hours significantly increases the risk of dangerous side effects, including severe hypotension, priapism, visual disturbances, and cardiovascular complications. Understanding the risks of sildenafil overdose and knowing when to seek emergency help can prevent potentially life-threatening outcomes and permanent tissue damage.

What Happens If You Take Too Much Sildenafil

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK for treating erectile dysfunction and pulmonary arterial hypertension. When taken at prescribed doses—typically 25 mg, 50 mg, or 100 mg for erectile dysfunction—sildenafil is generally well tolerated. However, taking more than the recommended dose significantly increases the risk of adverse effects and potentially serious complications.

The mechanism of action involves selective inhibition of PDE5, which leads to increased cyclic guanosine monophosphate (cGMP) levels in smooth muscle cells. This causes vasodilation, particularly in the corpus cavernosum of the penis, facilitating erection. Excessive doses amplify this vasodilatory effect throughout the body, potentially causing dangerous drops in blood pressure and cardiovascular strain.

Key risks of sildenafil overdose include:

• Severe hypotension (dangerously low blood pressure below 90/50 mmHg)

• Priapism (painful erection lasting more than 4 hours)

• Visual disturbances, including blue-tinged vision and photosensitivity, due to cross-inhibition of PDE6 in the retina

• Sudden hearing loss (with or without tinnitus)

• Cardiovascular complications, particularly in those with pre-existing heart conditions

• Increased severity of common side effects such as headache, flushing, and dizziness

The MHRA emphasises that sildenafil should only be taken as prescribed by a healthcare professional or supplied by a pharmacist (Viagra Connect) following appropriate assessment. Exceeding the maximum recommended dose of 100 mg in 24 hours for erectile dysfunction substantially elevates these risks. Individuals with cardiovascular disease, those taking nitrates, guanylate cyclase stimulators (e.g., riociguat), alpha-blockers, or certain other medications, and older adults are particularly vulnerable to serious complications from sildenafil overdose. There is no specific antidote for sildenafil overdose, making prevention and prompt medical attention essential.

Recognising Sildenafil Overdose Symptoms

Identifying the signs of sildenafil overdose promptly is crucial for seeking appropriate medical intervention. Symptoms typically manifest within 30 minutes to 2 hours of ingestion, corresponding with peak plasma concentrations, though the timing and severity depend on the amount taken and individual patient factors.

Cardiovascular symptoms are among the most concerning manifestations of sildenafil overdose. Patients may experience severe hypotension, presenting as profound dizziness, light-headedness, fainting, or syncope. Palpitations, chest pain, or tightness may occur, particularly in individuals with underlying cardiac conditions. The excessive vasodilation can compromise blood flow to vital organs, potentially leading to severe hypotension and, rarely, circulatory complications.

Visual disturbances represent another hallmark of sildenafil toxicity. Due to cross-inhibition of PDE6 in retinal tissue, patients may report blurred vision, increased sensitivity to light (photophobia), a blue tinge to vision (cyanopsia), or temporary vision loss. Non-arteritic anterior ischaemic optic neuropathy (NAION), though rare, has been reported and constitutes a medical emergency requiring immediate ophthalmological assessment.

Hearing changes such as sudden decrease or loss of hearing, sometimes accompanied by tinnitus or vertigo, require urgent medical attention and immediate discontinuation of sildenafil.

Priapism—a persistent, painful erection lasting more than 4 hours—is a urological emergency associated with excessive sildenafil. This condition can cause permanent damage to penile tissue and erectile function if not treated promptly. Other symptoms include severe headache, facial flushing more intense than typical, nasal congestion, gastrointestinal upset (nausea, vomiting, diarrhoea), and muscle aches.

In severe overdose, patients may experience confusion, seizures, or loss of consciousness. Any combination of these symptoms following sildenafil ingestion warrants immediate medical evaluation, particularly cardiovascular, visual, or hearing symptoms, which may indicate serious complications requiring urgent intervention.

What to Do If You've Taken Excess Sildenafil

If you suspect you have taken too much sildenafil, immediate action is essential to minimise potential harm. The appropriate response depends on the severity of symptoms, but erring on the side of caution is always advisable when dealing with medication overdose.

Immediate steps to take:

• Stop taking any further doses and do not attempt to 'counteract' the overdose with other medications

• Contact NHS 111 immediately for advice if you have mild symptoms or are uncertain about the severity

• Call 999 or go to A&E if you experience severe symptoms such as chest pain, fainting, vision loss, hearing loss, breathing difficulties, or priapism

• Do not drive yourself to hospital if experiencing dizziness, visual disturbances, or other impairing symptoms

• Important: If you experience chest pain after taking sildenafil, do not take nitrate medications (such as GTN spray). Tell emergency responders you have taken sildenafil

When seeking medical help, provide healthcare professionals with accurate information about the dose taken, timing of ingestion, and any other medications or substances consumed. Bring the medication packaging if possible. Be honest about the circumstances—healthcare professionals are there to help, not judge, and complete information is vital for appropriate treatment.

Medical management of sildenafil overdose is primarily supportive, as there is no specific antidote. Treatment may include cardiovascular monitoring, intravenous fluids for hypotension, and symptomatic relief. For priapism, urological intervention may be necessary, including aspiration of blood from the corpus cavernosum or injection of sympathomimetic agents. Haemodialysis is generally ineffective due to sildenafil's high protein binding.

If you have taken a moderately excessive dose but are asymptomatic, medical professionals may recommend observation and monitoring. However, never assume you are safe without professional assessment—some complications may develop gradually. Always seek medical advice via NHS 111 or your GP for guidance on any sildenafil overdose, regardless of perceived severity.

Safe Sildenafil Dosing and NHS Guidelines

Understanding appropriate sildenafil dosing is fundamental to safe use and preventing overdose. In the UK, sildenafil is available on NHS prescription for erectile dysfunction under specific circumstances, as Viagra Connect (50 mg) following pharmacist assessment, or privately through regulated pharmacies.

Standard dosing for erectile dysfunction:

• Starting dose: 50 mg taken approximately 1 hour before sexual activity

• Dose adjustment: May be increased to 100 mg or decreased to 25 mg based on efficacy and tolerability

• Maximum frequency: Once daily only—never exceed one dose in 24 hours

• Timing considerations: Effects typically last 4–6 hours; taking with high-fat meals may delay absorption

NICE guidance emphasises that sildenafil should be prescribed at the lowest effective dose. For older adults (over 65 years) or those with hepatic or severe renal impairment, a starting dose of 25 mg is recommended due to altered pharmacokinetics and increased sensitivity to adverse effects.

Special dosing considerations:

• With potent CYP3A4 inhibitors like ritonavir or cobicistat, do not exceed 25 mg in 48 hours

• With moderate CYP3A4 inhibitors (erythromycin, clarithromycin, itraconazole, verapamil), start at 25 mg

• If taking alpha-blockers, ensure you are on a stable dose and start sildenafil at 25 mg; monitor for postural hypotension

• Avoid grapefruit juice as it can increase sildenafil blood levels

Absolute contraindications include concurrent use of nitrates or nitric oxide donors (including recreational 'poppers' containing alkyl nitrites), guanylate cyclase stimulators (riociguat), recent stroke or myocardial infarction (within 6 months), unstable angina, severe heart failure, and hypotension (blood pressure below 90/50 mmHg). Sildenafil should never be combined with other PDE5 inhibitors or used recreationally.

The NHS advises obtaining sildenafil only through legitimate healthcare channels. Online purchases from unregulated sources carry significant risks, including counterfeit products with incorrect dosages, contamination, or dangerous additives. Legitimate UK online pharmacies require consultation with a registered pharmacist or prescriber and display the General Pharmaceutical Council (GPhC) logo. Always inform your GP or prescriber about all medications, supplements, and health conditions before starting sildenafil to ensure safe prescribing tailored to your individual circumstances.

Preventing Sildenafil Overdose and Misuse

Prevention of sildenafil overdose requires a combination of patient education, responsible prescribing, and awareness of risk factors. Understanding why overdose occurs and implementing practical safeguards significantly reduces the likelihood of adverse outcomes.

Common reasons for sildenafil overdose include:

• Intentionally exceeding prescribed doses in the mistaken belief that 'more is better'

• Taking additional doses too soon when the first dose appears ineffective

• Obtaining sildenafil from multiple sources without medical oversight

• Recreational misuse, often in combination with alcohol or illicit substances

• Accidental ingestion by children or vulnerable adults

Practical prevention strategies:

Store medication safely in original packaging, out of sight and reach of children and others who might accidentally or intentionally access it. Keep a record of doses taken to avoid confusion, particularly if you have memory difficulties.

Follow prescribing instructions precisely. If a dose seems ineffective, consult your prescriber rather than self-adjusting. Do not take more than one dose in 24 hours and never combine with other PDE5 inhibitors. Sildenafil requires sexual stimulation to work—it is not an aphrodisiac—and effectiveness can be influenced by psychological factors, timing, and food intake. Your healthcare provider can assess whether dose adjustment, timing changes, or alternative treatments are appropriate.

Avoid alcohol and recreational drugs when using sildenafil. Alcohol can impair erectile function and exacerbate hypotensive effects, whilst combining sildenafil with substances such as cocaine or MDMA significantly increases cardiovascular risks. Never share prescription medications with others, even if they report similar symptoms.

Regular medication reviews with your GP or pharmacist ensure sildenafil remains appropriate and safe, particularly if you develop new health conditions or start new medications. Be vigilant about potential drug interactions—inform all healthcare providers that you take sildenafil.

If you find yourself frequently tempted to exceed prescribed doses, discuss this openly with your healthcare provider. This may indicate that your current treatment is inadequate, and alternative approaches—including psychological support, different medications, or addressing underlying health issues—may be more effective and safer than increasing sildenafil doses beyond recommended limits.

If you experience any suspected side effects from sildenafil, report them to the MHRA through the Yellow Card Scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Frequently Asked Questions