Essential Sildenafil Safety: What to Avoid

Sildenafil, the active ingredient in both Viagra and generic sildenafil tablets, belongs to a group of medicines called PDE5 inhibitors. It works by increasing blood flow to the penis during sexual stimulation and is used to treat erectile dysfunction. However, some medicines and substances can interact with sildenafil. The most important example is nitrate medicines, such as GTN spray and isosorbide, which can cause a dangerous drop in blood pressure when taken with sildenafil. Alcohol, grapefruit, some blood pressure medicines and unlicensed supplements may also require caution.

For adults in the UK who are considering sildenafil or have been prescribed it for erectile dysfunction, this guide explains which medicines and substances to avoid or discuss with a healthcare professional, what to know about food and drink, which health conditions may require extra care, and how to use sildenafil safely. It also helps separate established safety concerns from common online claims, so you can make informed decisions about your treatment.

This information does not replace advice from your prescriber or pharmacist. However, it can help you understand why these precautions matter and what you should check before taking sildenafil.

Key things to know

• Nitrate medicines, including GTN spray and isosorbide, must not be taken with sildenafil because the combination can cause a dangerous drop in blood pressure.
• You can drink alcohol while taking sildenafil, but drinking heavily may make it harder to get or maintain an erection and may increase some side effects, according to NHS guidance.
• Grapefruit and grapefruit juice may increase sildenafil levels in the body, so it is sensible to avoid large amounts around the time you take sildenafil.
• Unlicensed "natural" sexual enhancement supplements can carry risks. The MHRA has warned about and seized illegal erectile dysfunction products, some of which may contain undeclared medicines at unknown strengths.
• Do not take more than one dose of sildenafil in 24 hours unless your prescriber has specifically advised you otherwise.

Nitrate Medications: The Most Dangerous Interaction

The most important combination to avoid with sildenafil is nitrate medicine. This includes glyceryl trinitrate (GTN) spray or tablets, isosorbide mononitrate, isosorbide dinitrate and other medicines containing nitrates. Recreational substances known as "poppers", which can contain alkyl nitrites, should also be avoided with sildenafil.

Both nitrates and sildenafil can lower blood pressure by widening blood vessels. Taking them together can cause a severe and potentially life threatening drop in blood pressure.

This is a recognised contraindication rather than a precaution to manage yourself. If you use nitrate medicines for angina or another heart condition, tell your prescriber before taking sildenafil. Sildenafil may not be suitable for you.

If you are unsure whether one of your medicines contains a nitrate, check with your doctor or pharmacist before taking sildenafil. Do not assume that a medicine is safe simply because it does not have "nitrate" in its name.

Alcohol and Sildenafil: What Is Actually Safe?

Alcohol is not contraindicated with sildenafil, according to NHS guidance. This means you do not necessarily need to avoid alcohol completely. However, drinking a large amount of alcohol can make it more difficult to get or maintain an erection and may make some sildenafil side effects, such as dizziness, headache, flushing or low blood pressure, more noticeable.

There is no specific "safe" number of alcohol units set for taking sildenafil. A sensible approach is to avoid heavy drinking, particularly around the time you plan to take sildenafil. If you notice that alcohol affects how well sildenafil works for you, consider reducing your intake and speak to your prescriber if you have concerns.

Grapefruit and Sildenafil: Why Does It Matter?

Grapefruit and grapefruit juice can affect enzymes involved in how sildenafil is broken down in the body. This may increase the amount of sildenafil in your bloodstream and could increase the likelihood of side effects such as headache, flushing or low blood pressure.

The size of this effect can vary depending on factors such as the amount of grapefruit consumed. For this reason, it is sensible to avoid large amounts of grapefruit or grapefruit juice around the time you take sildenafil rather than trying to work out an exact "safe" quantity.

If you regularly consume grapefruit or grapefruit juice, or if you take other medicines that may interact with sildenafil, mention this to your prescriber or pharmacist. They can advise you based on your full medication and health history.

Food, Meals and Timing

A heavy or high fat meal can slow down the absorption of sildenafil, which may mean that it takes longer to start working. It does not usually stop the medicine from working, but taking sildenafil on a relatively empty stomach may give you a more predictable onset.

You do not normally need to make any other specific changes to your diet when taking sildenafil. You can generally eat and drink as usual.

Other Medicines and Supplements to Be Cautious With

Apart from nitrates, several other medicines can affect how sildenafil works or increase the risk of side effects. Some antifungal medicines and CYP3A4 inhibitors, including ritonavir, can increase sildenafil levels by slowing its breakdown.

Medicines that lower blood pressure, particularly alpha blockers used for conditions such as high blood pressure or an enlarged prostate, can increase the risk of low blood pressure when taken with sildenafil. Riociguat should not be taken with sildenafil because the combination can cause a significant drop in blood pressure.

Sildenafil should also not normally be combined with other PDE5 inhibitors or other erectile dysfunction treatments unless a healthcare professional specifically advises you to do so. Taking these medicines together may increase the risk of side effects.

Before starting sildenafil, give your prescriber a complete list of everything you take. This includes prescription medicines, over the counter medicines, vitamins, herbal remedies and supplements. This helps them check for possible interactions and decide whether sildenafil is suitable for you.

Herbal remedies and supplements need particular care. NHS guidance notes that there is not enough information to confirm that herbal remedies and supplements are safe to take with sildenafil, as they are not tested and regulated in the same way as licensed medicines.

Extra caution is needed with products marketed as "natural" sexual enhancement or performance supplements. The MHRA has seized millions of doses of unlicensed erectile dysfunction products in recent years. Some of these products may contain undeclared medicines or unpredictable amounts of active ingredients, so you may not know exactly what you are taking or how it could interact with sildenafil.

For greater confidence that your medicine is genuine and supplied appropriately, obtain sildenafil through a GPhC registered UK pharmacy following an appropriate clinical assessment, rather than from an unregulated seller.

Health Conditions That Need Extra Caution

Some health conditions require a more careful assessment before sildenafil is prescribed, and in some situations sildenafil may not be suitable. These include significant cardiovascular disease, a recent heart attack or stroke, very low blood pressure and severe liver impairment.

Certain eye conditions may also require particular caution, including a history of non arteritic anterior ischaemic optic neuropathy, a condition associated with sudden loss of vision.

Tell your prescriber about any heart, blood pressure, liver, kidney or eye conditions you have, as well as any medicines you take. They can consider your medical history and decide whether sildenafil is appropriate for you.

Sildenafil is licensed in the UK for the treatment of erectile dysfunction in men. It is not licensed for the treatment of female sexual dysfunction.

This is why a proper clinical assessment is important before treatment. It allows your prescriber to consider your health, medicines and individual circumstances rather than treating the prescription as a simple formality.

Dosage Safety: What Not to Do

Do not take more than one dose of sildenafil in a 24 hour period unless your prescriber has specifically advised you otherwise. This applies even if you feel that your first dose has not worked as expected.

Sildenafil is available in 25mg, 50mg and 100mg strengths. Taking an additional tablet does not necessarily improve the effect and can increase the risk of side effects, including low blood pressure.

The usual starting dose for many adults is 50mg, although your prescriber may recommend a lower or higher strength depending on factors such as how well it works for you, side effects and other medicines you take.

If your current dose does not seem to be working well enough, speak to your prescriber rather than taking an extra tablet or changing your dose yourself. They can advise whether a different strength or another treatment option may be more appropriate.

When to Seek Immediate Medical Help

Seek urgent medical attention if you experience chest pain during or after sexual activity, a sudden loss or decrease in vision or hearing, or an erection lasting more than 4 hours, known as priapism.

These problems are uncommon but can require urgent treatment. Do not wait to see whether they resolve on their own.

More common side effects of sildenafil include headache, flushing, indigestion, nasal congestion and dizziness. These are often mild and temporary, but speak to your pharmacist or prescriber if they are troublesome, persistent or concerning.

If you develop symptoms that could indicate a serious reaction, including severe dizziness, fainting, chest pain or significant difficulty breathing, seek urgent medical help.

Available Treatments

Prices update live and may change.

When prescribed appropriately, sildenafil is an established treatment for erectile dysfunction. Long-term suitability should be reviewed periodically as part of ongoing care .

Medical Disclaimer

This page provides general information about sildenafil interactions, precautions and safe use. It is not a substitute for personalised medical advice, diagnosis or treatment.

Before starting sildenafil, tell your doctor, prescriber or pharmacist about all medicines, herbal remedies and supplements you take, including those bought without a prescription. This helps them check for possible interactions and assess whether sildenafil is suitable for you.

If you experience chest pain, sudden changes in your vision or hearing, or an erection lasting more than 4 hours, seek urgent medical attention. Always follow the instructions provided with your medicine and speak to a healthcare professional if you have any concerns about your treatment.