Sildenafil and Metformin: Can You Take Them Together?

Sildenafil and Metformin: What You Need to Know

Published: 16 October 2026

Many men wonder whether sildenafil and metformin can be taken together safely. The good news is that there is no direct interaction between sildenafil (Viagra) and metformin, the most commonly prescribed medicine for type 2 diabetes. However, because diabetes itself can affect erectile function and blood vessels, your prescriber will carefully review your overall health before recommending ED treatment.

What is sildenafil and metformin used for?

Sildenafil is a prescription medicine used to treat erectile dysfunction (ED). It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused [3]. Sildenafil is available in 25mg, 50mg and 100mg tablets, usually taken about one hour before sexual activity, with effects lasting around four to six hours. Sexual stimulation is still needed for the medicine to work.

Metformin is a prescription medicine used to manage type 2 diabetes. It works by reducing the amount of glucose (sugar) released by your liver and helping your body respond better to insulin. Metformin is usually taken once or twice daily with meals and is often the first medicine prescribed when diet and exercise alone are not enough to control blood sugar levels. It does not directly affect erectile function, but good diabetes control can help protect blood vessel health over time.

Can you take sildenafil and metformin together?

Yes, sildenafil and metformin can be taken together. No direct drug interaction between these two medicines has been reported in clinical practice or major drug databases [3]. Metformin does not affect how sildenafil is broken down in the body, and sildenafil does not interfere with metformin's blood-sugar-lowering effects. This means the combination is generally considered safe when both medicines are prescribed appropriately.

However, it is important to understand that having diabetes—especially if it is not well controlled—can itself contribute to erectile dysfunction. High blood sugar over time can damage blood vessels and nerves, making erections more difficult to achieve or maintain [1]. This is why your prescriber will want to know about your diabetes management, current blood sugar control, and any complications such as heart disease, kidney problems or nerve damage before prescribing sildenafil.

Why diabetes and ED often occur together

Erectile dysfunction is more common in men with diabetes than in the general population [10]. Diabetes can affect the blood vessels and nerves that are essential for achieving an erection. Over time, high blood sugar can lead to a condition called endothelial dysfunction, where the lining of blood vessels does not work properly, reducing blood flow to the penis. Nerve damage (neuropathy) can also reduce sensation and the signals needed for an erection. Managing your diabetes well—through medication, diet and lifestyle—can help reduce the risk of ED and improve your response to treatment.

What your prescriber checks before prescribing sildenafil with metformin

Even though sildenafil and metformin do not interact directly, your prescriber will carry out a thorough health check during your online consultation. They will ask about your diabetes control, how long you have had diabetes, and whether you have any complications such as heart disease, high blood pressure, high cholesterol, kidney problems or eye disease. These conditions are more common in people with diabetes and can affect whether sildenafil is suitable for you.

Your prescriber will also review all your other medicines. Some medicines used alongside metformin—such as blood pressure tablets, alpha-blockers for prostate symptoms, or certain antibiotics—can interact with sildenafil [3]. For example, alpha-blockers (like tamsulosin or doxazosin) can increase the risk of dizziness or low blood pressure when combined with sildenafil, so your prescriber may start you on a lower dose. It is essential to list every medicine you take, including over-the-counter products and supplements, so your prescriber can check for interactions and choose the safest treatment plan.

Medicines that must not be taken with sildenafil and metformin

While sildenafil and metformin are safe together, there are some medicines you must never take with sildenafil because they can cause a dangerous drop in blood pressure. Do not take sildenafil if you are using nitrates (such as GTN spray, isosorbide mononitrate or isosorbide dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites) [3]. You should also never take two different PDE5 inhibitors (such as sildenafil and tadalafil) at the same time.

If you take any of these medicines, tell your prescriber immediately. The combination can lead to a severe and potentially life-threatening fall in blood pressure. Similarly, if you are prescribed a nitrate medicine after starting sildenafil, inform the prescribing doctor that you are using ED treatment. Your pharmacist and prescriber are here to help you navigate these safety checks during your consultation.

Other medicines that need careful checking

Some medicines can raise the level of sildenafil in your blood, increasing the risk of side effects. These include potent CYP3A4 inhibitors such as ritonavir, cobicistat (found in some HIV medicines), ketoconazole, itraconazole and clarithromycin [3]. If you take any of these, your prescriber may recommend a lower starting dose of sildenafil or choose an alternative ED treatment. Conversely, medicines that speed up the breakdown of sildenafil—such as rifampicin, carbamazepine, phenytoin or St John's wort—can make it less effective. Always declare every medicine during your consultation so your prescriber can tailor your treatment safely.

Practical advice for taking sildenafil and metformin safely

Take sildenafil about one hour before you plan to have sex, on an empty stomach or after a light meal; a heavy or high-fat meal can delay how quickly it works [3]. You can take your metformin as usual, with meals, at the times your doctor has prescribed. There is no need to separate the two medicines or adjust the timing of your metformin dose when using sildenafil.

Keep your diabetes well controlled. Good blood sugar management protects your blood vessels and nerves, which can improve your response to ED treatment and your overall sexual health [1]. Attend your regular diabetes reviews, monitor your blood sugar as advised, and follow a healthy diet and exercise plan. Avoid drinking large amounts of alcohol, as heavy drinking can worsen erectile dysfunction and add to the blood-pressure-lowering effect of sildenafil, increasing the risk of dizziness or fainting.

If you experience side effects such as headache, flushing, indigestion or a stuffy nose, these are common and usually mild [3]. However, seek urgent medical help if you have an erection lasting more than four hours, sudden loss of vision or hearing, or chest pain during sex. If you feel dizzy or light-headed after taking sildenafil, sit or lie down and avoid driving or operating machinery until you feel better.

How to get sildenafil and metformin prescribed safely online

At Cured Pharmacy, a GPhC-registered online pharmacy, you can request sildenafil after completing a short online consultation. A UK-registered prescriber will review your answers, including your diabetes history, current medicines (such as metformin), and any other health conditions. If sildenafil is suitable and safe for you, your prescription will be dispensed by our pharmacy team and delivered discreetly to your door.

Your metformin should continue to be prescribed by your GP or diabetes specialist, as they monitor your blood sugar control and adjust your dose as needed. Never stop or change your diabetes medicine without speaking to your doctor. If your ED treatment needs change, or if you start a new medicine, update your prescriber during your next consultation. Our team is here to support you with clear advice and safe, effective treatment tailored to your health.

Why see your GP about new erectile dysfunction

If you are experiencing erectile dysfunction for the first time, it is important to see your GP for a full assessment [1]. ED can be an early warning sign of cardiovascular disease or poorly controlled diabetes, and your GP can arrange blood tests (including HbA1c to check your diabetes control, cholesterol and kidney function) and a blood pressure check. Treating the underlying cause—such as improving your diabetes management or addressing high blood pressure—can sometimes improve erectile function on its own and will protect your long-term health. Once your GP has assessed you, an online consultation for ED treatment can be a convenient and private way to access ongoing prescriptions.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 16 October 2026]
2. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 16 October 2026]
3. Feldman, H. A., Goldstein, I., Hatzichristou, D. G., Krane, R. J., & McKinlay, J. B. (1994). Impotence and its medical and psychosocial correlates: Results of the Massachusetts Male Aging Study. Journal of Urology, 151(1), 54–61. https://pubmed.ncbi.nlm.nih.gov/8254833/ [accessed 16 October 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.