Tadalafil and Cimetidine: Can You Take Them Together?

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Tadalafil and Cimetidine: Understanding the Interaction

Published: 19 October 2026

Tadalafil and cimetidine can be taken together, but cimetidine may raise the level of tadalafil in your bloodstream, which means your prescriber will need to adjust your dose to keep treatment safe and effective. Tadalafil is a PDE5 inhibitor used to treat erectile dysfunction (ED), while cimetidine is an older medicine for heartburn and stomach ulcers that affects how the liver breaks down many other drugs. This page explains how the interaction works, what your prescriber will check during your consultation, and the practical steps you can take to use both medicines safely.

What Is Tadalafil and How Does It Work?

Tadalafil (the active ingredient in Cialis) is a prescription medicine licensed in the UK to treat erectile dysfunction in men [4]. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing the blood vessels in the penis, allowing more blood to flow in when you are sexually aroused. Tadalafil does not cause an erection on its own—you still need sexual stimulation for it to work.

Tadalafil is available in two ways: on-demand tablets (usually 10 mg or 20 mg) taken at least 30 minutes before sex, with effects lasting up to 36 hours, and daily low-dose tablets (2.5 mg or 5 mg) taken every day at the same time [4]. The long duration of action is why tadalafil is sometimes called the 'weekend pill'. Common side effects include headache, indigestion, back pain, and flushing, which are usually mild and short-lived.

Your body breaks down tadalafil mainly through an enzyme system in the liver called CYP3A4 [4]. This is important because medicines that slow down or speed up this enzyme can change how much tadalafil stays in your bloodstream, which is exactly what happens when you take cimetidine at the same time.

What Is Cimetidine and Why Is It Prescribed?

Cimetidine is a medicine known as an H2 receptor antagonist (or H2 blocker) that reduces the amount of acid your stomach produces. It has been used for many years to treat heartburn, indigestion, stomach ulcers, and gastro-oesophageal reflux disease (GORD). Cimetidine is available on prescription and can also be bought over the counter at lower doses for short-term relief of heartburn.

Although cimetidine is effective, it is prescribed less often today because newer medicines such as proton pump inhibitors (like omeprazole or lansoprazole) tend to work better and have fewer drug interactions. However, some people still take cimetidine, especially if other treatments have not suited them or if it has been used successfully in the past.

One important feature of cimetidine is that it affects several liver enzymes, including CYP3A4, CYP2D6, and CYP1A2, which are responsible for breaking down many different medicines. This means cimetidine can raise the blood levels of other drugs you take, including tadalafil, and your prescriber needs to be aware of this interaction to adjust doses safely.

How Do Tadalafil and Cimetidine Interact?

The interaction between tadalafil and cimetidine happens because cimetidine slows down the liver enzyme (CYP3A4) that normally breaks down tadalafil [4]. When this enzyme works more slowly, tadalafil stays in your body for longer and reaches higher levels in your bloodstream. This does not mean the combination is unsafe, but it does mean your dose of tadalafil may need to be lower to avoid an increased risk of side effects such as headache, dizziness, flushing, or a drop in blood pressure.

The British National Formulary notes that cimetidine is a moderate inhibitor of CYP3A4, and the manufacturer's information for tadalafil advises caution when it is used alongside such medicines [4]. In practice, your prescriber will review the dose of both medicines during your consultation and may start you on a lower dose of tadalafil—often 10 mg instead of 20 mg for on-demand use, or they may recommend the daily low-dose option if that suits your needs better.

It is important to tell your prescriber or pharmacist about all the medicines you take, including those bought over the counter, because cimetidine can interact with many drugs. If you are already taking tadalafil and your GP then prescribes cimetidine (or you buy it from a pharmacy), let them know so they can check whether any dose adjustment is needed. Never stop or change a prescribed medicine without professional advice.

Why This Interaction Matters in Practice

Higher tadalafil levels can increase the chance of side effects, particularly low blood pressure, which may cause dizziness or fainting, especially when you stand up quickly. If you also take other medicines that lower blood pressure—such as alpha-blockers for an enlarged prostate, or treatments for high blood pressure—the combined effect needs careful monitoring. Your prescriber will check your full medication list and medical history during the online consultation to ensure tadalafil is safe and appropriately dosed for you.

What Your Prescriber Will Check During Your Consultation

When you request tadalafil through Cured Pharmacy, a UK-registered prescriber reviews your online consultation before any medicine is supplied. They will ask about all your current medicines, including cimetidine and any other over-the-counter treatments, herbal supplements, or vitamins. This is essential because some combinations—such as tadalafil with nitrates, nicorandil, riociguat, or recreational drugs called 'poppers'—are dangerous and must never be used together [4].

Your prescriber will also check your medical history, including any heart problems, recent stroke or heart attack, blood pressure (both high and low), liver or kidney disease, and any history of priapism (a prolonged, painful erection) or eye conditions such as non-arteritic anterior ischaemic optic neuropathy (NAION) [4]. If you take cimetidine, the prescriber will consider whether a lower starting dose of tadalafil is appropriate, and they may recommend the 10 mg on-demand tablet or the daily 2.5 mg or 5 mg option.

If you are also taking an alpha-blocker such as tamsulosin or doxazosin (commonly prescribed for urinary symptoms related to an enlarged prostate), your prescriber will ensure you are stable on that medicine before starting tadalafil, and they will choose the lowest effective dose to minimise the risk of dizziness or fainting [4]. The consultation is designed to be thorough but straightforward, and you can complete it online at a time that suits you.

Practical Advice for Taking Tadalafil with Cimetidine

If your prescriber approves tadalafil while you are taking cimetidine, follow the dose and timing instructions exactly as given. For on-demand tadalafil, take your tablet at least 30 minutes before you plan to have sex; the effect can last up to 36 hours, so you do not need to rush [4]. For daily tadalafil, take one tablet at the same time each day, whether or not you are planning sexual activity. You still need sexual stimulation for the medicine to work—it will not cause an automatic erection.

Avoid drinking large amounts of alcohol when using tadalafil, as heavy drinking can make erectile dysfunction worse and add to the blood-pressure-lowering effect, increasing the risk of dizziness [4]. Grapefruit juice can also raise tadalafil levels, so it is best to avoid it or discuss it with your pharmacist. If you experience side effects such as a severe headache, dizziness, or visual disturbances, contact your GP or pharmacist for advice.

Do not take more than one dose of on-demand tadalafil in 24 hours, and never combine tadalafil with another PDE5 inhibitor such as sildenafil (Viagra) or vardenafil (Levitra) [4]. If you need to start or stop cimetidine while you are taking tadalafil, let your prescriber know so they can review whether your tadalafil dose needs adjusting. Keep all your medicines in their original packaging, out of reach of children, and check the expiry date before use.

When to Seek Medical Advice

Seek urgent medical help if you develop an erection that lasts longer than four hours (priapism), sudden loss of vision or hearing, or chest pain during sex [4]. These are rare but serious side effects that need immediate attention. If you feel dizzy or faint, sit or lie down until the feeling passes, and mention it to your prescriber at your next review. For any new or worsening symptoms, contact your GP or call NHS 111 for advice.

Alternatives and Other Considerations

If the interaction between tadalafil and cimetidine is a concern, your prescriber may suggest switching to a different medicine for heartburn or indigestion that has fewer drug interactions. Proton pump inhibitors such as omeprazole or lansoprazole are often preferred today and do not significantly affect tadalafil levels [4]. Alternatively, other H2 blockers such as ranitidine (though currently unavailable in the UK) or famotidine may have a smaller effect on liver enzymes, but your GP or pharmacist will advise on the best option for your individual situation.

If tadalafil is not suitable for you, there are other PDE5 inhibitors available, including sildenafil (Viagra), vardenafil (Levitra), and avanafil (Spedra) [3][5][6]. Each has a slightly different profile in terms of how quickly it works and how long it lasts, and your prescriber can help you choose the one that fits your lifestyle and medical history. All PDE5 inhibitors are affected to some degree by medicines that inhibit CYP3A4, so the same caution applies if you take cimetidine.

Remember that erectile dysfunction can be an early warning sign of underlying health conditions such as heart disease or diabetes, so if you are experiencing ED for the first time, it is important to see your GP for a full assessment [1][2]. Lifestyle changes—such as losing weight if needed, exercising regularly, stopping smoking, and reducing alcohol—can also improve erectile function and overall health. Cured Pharmacy offers a confidential online consultation with UK prescribers, and all prescription medicines are dispensed by our GPhC-registered pharmacy (GPhC 9012511).

How Cured Pharmacy Can Help

At Cured Pharmacy, you can request tadalafil and other ED treatments through a simple online consultation reviewed by a UK-registered prescriber. We stock a range of options, including generic tadalafil from £7.95 and branded Cialis from £12.00 (first order with code Ednew: £6.36 and £9.60 respectively). All orders are delivered discreetly to your door, and our pharmacist-led service is here to answer any questions about your treatment and how it fits with your other medicines.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 19 October 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 19 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 19 October 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 19 October 2026]
5. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 19 October 2026]
6. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 19 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.

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