Tadalafil and Clarithromycin: Can You Take Them Together?

Tadalafil and Clarithromycin: Understanding the Interaction

Published: 19 October 2026

Tadalafil and clarithromycin can interact because clarithromycin is a potent enzyme inhibitor that raises the level of tadalafil in your bloodstream. This doesn't mean you can't take them together, but it does mean your prescriber will need to adjust your tadalafil dose to keep treatment safe and effective. Understanding how these medicines interact helps you use them confidently while minimising the risk of side effects.

What is tadalafil and how does it work?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men [4]. It belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors, which work by relaxing the blood vessels in the penis, allowing more blood to flow in when you're sexually aroused [1].

Tadalafil is available in two forms: on-demand tablets (usually 10mg or 20mg) taken at least 30 minutes before sexual activity, with effects lasting up to 36 hours, and daily tablets (2.5mg or 5mg) taken once a day at the same time [4]. Both forms require sexual stimulation to work—tadalafil won't cause an erection on its own.

The medicine is broken down (metabolised) in your liver by an enzyme called CYP3A4 [4]. This is important because certain other medicines, including some antibiotics like clarithromycin, can slow down this enzyme and change how much tadalafil stays in your body.

What is clarithromycin and why might you be taking it?

Clarithromycin is a macrolide antibiotic commonly prescribed to treat bacterial infections such as chest infections, pneumonia, skin infections, and Helicobacter pylori (a stomach bacteria linked to ulcers). It works by stopping bacteria from growing and multiplying.

Clarithromycin is usually taken as a tablet or liquid twice a day for 5 to 14 days, depending on the type and severity of infection. Most people tolerate it well, though common side effects can include nausea, diarrhoea, and changes in taste.

Importantly, clarithromycin is a potent inhibitor of the CYP3A4 enzyme in your liver—the same enzyme responsible for breaking down tadalafil and many other medicines. This means clarithromycin can significantly increase the levels of tadalafil in your bloodstream, raising the risk of side effects if the dose isn't adjusted.

How do tadalafil and clarithromycin interact?

When you take tadalafil and clarithromycin together, the clarithromycin slows down the enzyme (CYP3A4) that normally breaks down tadalafil in your liver [4]. As a result, tadalafil stays in your body longer and reaches higher levels in your blood than it would on its own.

Higher tadalafil levels can increase the chance of side effects such as headache, flushing, indigestion, back pain, muscle aches, dizziness, and a drop in blood pressure. In rare cases, very high levels may lead to more serious problems like prolonged erections (priapism) or visual disturbances.

This interaction is well recognised and manageable. The British National Formulary advises that when tadalafil is used with potent CYP3A4 inhibitors like clarithromycin, the maximum dose of tadalafil should be reduced [4]. Your prescriber will take this into account during your consultation to ensure you receive a safe and effective dose.

What happens in plain English

Think of CYP3A4 as a clean-up crew in your liver that removes tadalafil from your system. Clarithromycin temporarily puts some of that crew out of action, so tadalafil hangs around longer and builds up to higher levels. Your prescriber compensates by giving you a lower dose of tadalafil, so the final amount in your blood stays in the safe and effective range.

What your prescriber checks before prescribing tadalafil and clarithromycin

If you're already taking clarithromycin (or start it while using tadalafil), your prescriber will review your full medication list and medical history. They'll check for any other medicines that might interact, your blood pressure, and whether you have any heart, liver, or kidney conditions that could affect how your body handles these medicines.

For men taking clarithromycin, the maximum recommended dose of on-demand tadalafil is typically 10mg in any 72-hour period [4]. If you're on daily tadalafil, your prescriber may advise a lower dose or a temporary break from tadalafil while you complete your antibiotic course, depending on your individual circumstances.

Your prescriber will also ask about other medicines that can interact dangerously with tadalafil—such as nitrates (GTN spray, isosorbide), nicorandil, riociguat, or recreational drugs known as 'poppers'—because these combinations can cause a severe drop in blood pressure and must never be taken together [3][4]. Alpha-blockers (such as tamsulosin or doxazosin) and other blood-pressure medicines will also be reviewed, as they can add to the blood-pressure-lowering effect of tadalafil.

Practical advice for taking tadalafil with clarithromycin

If your GP or another doctor prescribes clarithromycin and you're already using tadalafil, tell them immediately. Similarly, if you're taking clarithromycin and want to start tadalafil for ED, declare the antibiotic during your online consultation at Cured Pharmacy so the prescriber can adjust your dose safely.

Follow the dose your prescriber gives you exactly—do not take extra tadalafil thinking the antibiotic has 'weakened' it. In fact, the opposite is true: clarithromycin makes tadalafil stronger, so a lower dose is often needed. If you experience side effects such as severe headache, dizziness, prolonged erection (lasting more than four hours), or sudden vision or hearing loss, stop taking tadalafil and seek medical help straight away.

Clarithromycin courses are usually short (5–14 days), so any dose adjustment is temporary. Once you finish the antibiotic and it has cleared your system (usually within a few days), your prescriber can review whether your usual tadalafil dose can be resumed. Never stop a prescribed antibiotic early without medical advice, even if you feel better.

Tips to minimise side effects

Take tadalafil and clarithromycin at different times of day if possible (for example, clarithromycin with meals and tadalafil before planned sexual activity) to spread out any side effects. Avoid drinking grapefruit juice, as it can also raise tadalafil levels. Limit alcohol, which can worsen ED and add to the blood-pressure-lowering effect of tadalafil. Stay well hydrated and avoid getting up too quickly from sitting or lying down to reduce dizziness.

Other antibiotics and erectile dysfunction treatments

Not all antibiotics interact with tadalafil in the same way. Clarithromycin is a potent CYP3A4 inhibitor, but other macrolide antibiotics such as erythromycin also inhibit this enzyme (though usually less strongly) and may require dose adjustments. Azithromycin, another macrolide, has a much weaker effect on CYP3A4 and is less likely to cause a significant interaction.

Common antibiotics like amoxicillin, penicillin, trimethoprim, and nitrofurantoin do not inhibit CYP3A4 and are not expected to interact with tadalafil in the same way. However, every medicine you take—prescription, over-the-counter, or herbal—should be declared during your consultation so your prescriber can check for any potential interactions.

If you're prescribed a different antibiotic and are unsure whether it interacts with your ED treatment, ask your pharmacist or prescriber. The same principles apply to other PDE5 inhibitors: sildenafil, vardenafil, and avanafil are all metabolised by CYP3A4, so clarithromycin can affect them too [3][5][6]. Vardenafil and avanafil are particularly sensitive, and their use with potent CYP3A4 inhibitors is often contraindicated or requires significant dose reduction [5][6].

Choosing the right ED treatment during antibiotic therapy

If you need short-term antibiotic treatment and are concerned about interactions, discuss your options with your prescriber. In some cases, a brief pause in ED treatment or switching to a lower dose may be the safest approach. Alternatively, your prescriber may recommend a different PDE5 inhibitor or timing strategy. At Cured Pharmacy, our UK-registered prescribers review every consultation individually to find the safest, most effective solution for you.

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. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 19 October 2026]
3. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 19 October 2026]
4. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 19 October 2026]
5. 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.