Tadalafil and Allopurinol: Can You Take Them Together?

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What Is Tadalafil and How Does It Work?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men. 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][4].

Tadalafil is available as the branded medicine Cialis and as generic versions. It can be taken on-demand (usually 10mg or 20mg at least 30 minutes before sexual activity, with effects lasting up to 36 hours) or as a lower daily dose (2.5mg or 5mg) [4]. Unlike some ED treatments, tadalafil does not cause an erection by itself—sexual stimulation is still needed.

Common side effects include headache, indigestion, back pain, muscle aches, flushing, and a blocked or runny nose. These are usually mild and temporary. Tadalafil is only supplied after an online consultation reviewed by a UK prescriber, who will check it is safe and suitable for you.

What Is Allopurinol and Why Is It Prescribed?

Allopurinol is a prescription medicine used to prevent gout attacks and to treat high levels of uric acid in the blood (hyperuricaemia). Gout is a type of arthritis that causes sudden, severe joint pain, often in the big toe, caused by a build-up of uric acid crystals.

Allopurinol works by reducing the amount of uric acid your body produces. It is usually taken once daily as a long-term treatment to prevent gout flare-ups, rather than to treat an acute attack. Common doses range from 100mg to 300mg daily, though some people may need higher doses.

Side effects can include skin rashes (which should be reported to your doctor promptly), upset stomach, headaches, and changes in liver function tests. Allopurinol is generally well tolerated and is one of the most commonly prescribed medicines for gout prevention in the UK.

When to get urgent help

• Erection lasting more than 4 hours (priapism) – go to A&E immediately
• Sudden loss of vision or hearing – seek urgent medical attention
• Chest pain during sexual activity – stop and call 999
• Severe skin rash with fever while taking allopurinol – stop medicine and contact doctor immediately
• Symptoms of very low blood pressure: severe dizziness, fainting, confusion – seek urgent help

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.

Is There an Interaction Between Tadalafil and Allopurinol?

No major interaction is commonly reported between tadalafil and allopurinol. These two medicines work through completely different mechanisms in the body: tadalafil affects blood flow to the penis by inhibiting the PDE5 enzyme, while allopurinol reduces uric acid production by inhibiting the enzyme xanthine oxidase.

Because they do not share metabolic pathways or have overlapping effects on blood pressure or heart function, taking tadalafil and allopurinol together is not expected to cause problems for most men. However, every person's medical situation is unique, and your prescriber will review your full medication list and health history during your consultation.

It is important to declare all medicines you take—including over-the-counter products, herbal remedies, and supplements—when requesting ED treatment. This allows the prescriber to check for any potential issues specific to your circumstances and ensure tadalafil is safe for you.

How the Prescriber Assesses Your Suitability

During your online consultation, the prescriber will ask about your current medicines, medical conditions, and cardiovascular health. They will check whether you have any conditions that make tadalafil unsuitable, such as recent heart attack or stroke, severe heart failure, very low blood pressure, or if you take nitrates or nicorandil (which must never be combined with tadalafil).

If you take allopurinol for gout, the prescriber will also consider whether gout or its underlying causes (such as kidney disease or cardiovascular risk factors) affect your suitability for ED treatment. This comprehensive review ensures that tadalafil is both safe and likely to be effective for you.

What Your Prescriber Checks When You Take Tadalafil and Allopurinol

Even though no major interaction exists between tadalafil and allopurinol, your prescriber will still carry out important safety checks. They will review your cardiovascular health, as ED can be an early warning sign of heart disease or diabetes [1][2]. If you have not seen your GP about ED before, you may be encouraged to do so for a full health check.

The prescriber will confirm you are not taking any medicines that are contraindicated with tadalafil. These include nitrates (such as GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, and amyl or alkyl nitrites (poppers). Combining tadalafil with any of these can cause a dangerous fall in blood pressure [3][4].

If you take other blood-pressure medicines or alpha-blockers (such as doxazosin or tamsulosin for prostate symptoms), the prescriber will check you are stable on these treatments and may recommend starting tadalafil at a lower dose to minimise the risk of dizziness or low blood pressure. They will also ask about any history of priapism (prolonged erections), eye problems, or severe liver or kidney disease.

Practical Advice for Taking Tadalafil Safely with Allopurinol

If you have been prescribed both tadalafil and allopurinol, take each medicine exactly as directed. Allopurinol is usually taken once daily, often in the morning, and should be continued long-term to prevent gout. Tadalafil can be taken on-demand before sexual activity or as a daily low dose, depending on which regimen your prescriber recommends.

You do not need to separate the doses of tadalafil and allopurinol, as there is no timing-related interaction. However, if you take tadalafil on-demand, remember it works best when taken at least 30 minutes before sex (effects can last up to 36 hours), and you will still need sexual stimulation for it to work [4].

Avoid drinking large amounts of alcohol when using tadalafil, as heavy drinking can worsen erectile dysfunction and increase the risk of side effects such as dizziness and low blood pressure. Grapefruit juice may also raise tadalafil levels in your blood, so it is best to avoid it. Stay well hydrated, especially if you are taking allopurinol, as this helps prevent kidney stones.

If you develop any new symptoms or side effects, contact your GP or pharmacist. Do not stop taking allopurinol suddenly without medical advice, as this can trigger a gout flare-up.

When to Seek Urgent Medical Help

Seek immediate medical attention if you experience an erection lasting more than four hours (priapism), sudden loss of vision or hearing, or chest pain during sexual activity. These are rare but serious side effects that require urgent treatment.

If you develop a severe skin rash while taking allopurinol (especially if accompanied by fever or feeling unwell), stop the medicine and contact your doctor immediately, as this can occasionally indicate a serious allergic reaction.

Other Medicines and Conditions to Discuss with Your Prescriber

While tadalafil and allopurinol can usually be taken together, it is essential to tell your prescriber about all your current medicines. Some drugs can interact with tadalafil and require dose adjustments or extra monitoring.

Alpha-blockers (doxazosin, tamsulosin, alfuzosin, terazosin, prazosin, silodosin, indoramin) can increase the risk of low blood pressure and dizziness when combined with tadalafil. If you take an alpha-blocker, you should be stable on it before starting tadalafil, and your prescriber will usually recommend the lowest effective dose of the ED medicine [3][4].

Potent CYP3A4 inhibitors—such as ritonavir, cobicistat (found in some HIV medicines), ketoconazole, itraconazole, and clarithromycin—can raise tadalafil levels in your blood. Your prescriber may need to reduce the maximum dose of tadalafil or advise caution. Conversely, CYP3A4 inducers like rifampicin, carbamazepine, phenytoin, and St John's wort can make tadalafil less effective.

Declare any heart conditions, recent heart attack or stroke, angina, very low or high blood pressure, liver or kidney disease, blood disorders, stomach ulcers, or any history of priapism or eye problems (especially NAION, a sudden loss of vision). These factors will influence whether tadalafil is suitable and which dose is safest for you [2][4].

Can Gout or Its Treatment Affect Erectile Function?

Gout itself does not directly cause erectile dysfunction, but the conditions that often accompany gout—such as obesity, high blood pressure, diabetes, high cholesterol, and kidney disease—are all risk factors for ED [1][10]. Managing these underlying health issues can improve both gout control and erectile function.

Allopurinol does not cause erectile dysfunction. If you notice changes in your sexual function, discuss them with your GP, as they may be related to other health factors or medicines rather than your gout treatment.

In summary

• No major interaction is commonly reported between tadalafil and allopurinol
• Your prescriber reviews all medicines and health conditions during consultation
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers
• Tadalafil requires sexual stimulation to work and can last up to 36 hours
• Seek urgent help for erections over 4 hours or sudden vision or hearing loss

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