Tadalafil and Flucloxacillin: Can You Take Them Together?

Tadalafil and Flucloxacillin: Understanding the Interaction

Published: 21 October 2026

Many men wonder whether tadalafil and flucloxacillin can be taken together safely. The good news is that no major interaction between tadalafil (the active ingredient in Cialis) and flucloxacillin (a penicillin-type antibiotic) is commonly reported in clinical practice. However, your prescriber will still check your full medication list during your consultation to ensure the combination is appropriate for you personally, as individual health factors always matter.

What is tadalafil and flucloxacillin used for?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction (ED). It works by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused [4]. Tadalafil is available as on-demand tablets (10mg or 20mg, taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5mg or 5mg). It requires sexual stimulation to work and does not cause an automatic erection.

Flucloxacillin is a narrow-spectrum penicillin antibiotic commonly prescribed in the UK to treat bacterial infections, particularly those caused by staphylococcal bacteria. It is often used for skin and soft-tissue infections (such as cellulitis, impetigo, or infected wounds), bone infections, and respiratory tract infections. Flucloxacillin is usually taken four times a day, ideally on an empty stomach (30–60 minutes before food or two hours after), and courses typically last five to seven days depending on the infection being treated.

Is there an interaction between tadalafil and flucloxacillin?

No clinically significant interaction between tadalafil and flucloxacillin is commonly reported in the British National Formulary or major drug-interaction databases [4]. Flucloxacillin does not affect the liver enzymes (CYP3A4) that break down tadalafil, so it is unlikely to raise or lower tadalafil levels in your bloodstream. Similarly, tadalafil does not interfere with the way flucloxacillin works to fight bacterial infections.

That said, every person's health situation is unique. During your online consultation at Cured Pharmacy, the prescriber will review your complete medical history and all current medicines—including antibiotics—to ensure tadalafil is safe and suitable for you. If you are unwell with an infection, you may also feel less interested in sexual activity or experience temporary tiredness, which can affect how well ED treatment works for you.

How does the prescriber check safety?

When you request tadalafil through Cured Pharmacy, a UK-registered prescriber reviews your online consultation form. They will check for any medicines that do interact dangerously with tadalafil—such as nitrates (GTN spray, isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called poppers—because these combinations can cause a serious drop in blood pressure [4]. The prescriber will also look at other medicines that may need dose adjustments, such as alpha-blockers (e.g. tamsulosin, doxazosin) or potent CYP3A4 inhibitors (e.g. ritonavir, clarithromycin, ketoconazole). Flucloxacillin does not fall into any of these high-risk categories, but it is still essential to declare every medicine, supplement, and over-the-counter product you are taking.

Can you take tadalafil and flucloxacillin at the same time?

Yes, in most cases you can take tadalafil and flucloxacillin together, provided your prescriber has reviewed your full medical history and confirmed that tadalafil is suitable for you. There is no need to separate the doses by a specific number of hours, as the two medicines work in completely different ways and do not interfere with each other's absorption or effectiveness.

However, it is worth remembering that flucloxacillin is best absorbed on an empty stomach, so you should ideally take it 30–60 minutes before food or at least two hours after eating. Tadalafil, on the other hand, can be taken with or without food. If you are taking tadalafil daily (2.5mg or 5mg), you can continue your usual schedule while completing your flucloxacillin course. If you are using on-demand tadalafil (10mg or 20mg), take it at least 30 minutes before planned sexual activity, regardless of when you last took your antibiotic dose.

If you feel unwell or feverish due to your infection, you may find that your interest in sex is reduced or that tadalafil does not work as well as usual. This is a normal response to illness and does not mean the medicine has stopped working. Once you have recovered from the infection, you should notice your usual response to tadalafil returning.

What should you tell your prescriber about tadalafil and flucloxacillin?

Always declare flucloxacillin (or any other antibiotic) when you complete your online consultation for tadalafil. Even though no major interaction is expected, your prescriber needs a complete picture of your health to make a safe decision. Mention the dose of flucloxacillin you are taking, how long your course will last, and what infection you are being treated for.

You should also tell the prescriber about any other medicines you take regularly, including over-the-counter painkillers, herbal supplements (such as St John's wort), blood-pressure medicines, treatments for an enlarged prostate, and any recreational substances. If you have recently had a heart attack or stroke, have unstable angina, severe heart failure, very low blood pressure, or a history of sudden vision loss (NAION), tadalafil may not be suitable for you [4]. The prescriber will also ask about allergies, particularly if you have ever had an allergic reaction to penicillin antibiotics or PDE5 inhibitors.

What if you are prescribed a different antibiotic?

Some antibiotics do interact with tadalafil. For example, clarithromycin (a macrolide antibiotic) is a potent CYP3A4 inhibitor and can significantly raise tadalafil levels in your blood, which may increase the risk of side effects such as headache, flushing, or low blood pressure [4]. If you are prescribed clarithromycin, your doctor may reduce your tadalafil dose or advise you to pause treatment temporarily. Similarly, erythromycin (another macrolide) can have a moderate effect on tadalafil levels. Always check with your prescriber or pharmacist if you are started on a new antibiotic while taking tadalafil, and never assume that all antibiotics behave the same way.

Practical advice for taking tadalafil and flucloxacillin together

If you have been prescribed both medicines, continue to take flucloxacillin exactly as your doctor instructed—usually four times a day on an empty stomach—until you finish the full course, even if you start to feel better. Stopping antibiotics early can allow the infection to return and may contribute to antibiotic resistance. Take tadalafil as directed by your prescriber: if you are using the on-demand dose, take it at least 30 minutes before sex (and remember that sexual stimulation is needed for it to work); if you are on the daily dose, take one tablet at roughly the same time each day.

Avoid drinking large amounts of alcohol while taking tadalafil, as alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect of the medicine, making you feel dizzy or lightheaded [4]. Heavy drinking can also irritate your stomach and may reduce the effectiveness of flucloxacillin. Stay well hydrated, especially if you have a fever or infection, and avoid grapefruit juice, which can raise tadalafil levels in your blood.

If you experience side effects from either medicine—such as diarrhoea or stomach upset from flucloxacillin, or headache and flushing from tadalafil—these are usually mild and temporary. However, if you develop a severe allergic reaction (rash, swelling of the face or throat, difficulty breathing), stop both medicines and seek urgent medical help. Similarly, if you experience chest pain during sex, an erection lasting more than four hours, or sudden loss of vision or hearing, call 999 or go to A&E immediately [4].

How to get tadalafil safely while taking flucloxacillin

Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering a convenient, confidential service for erectile dysfunction treatment. To request tadalafil, complete a short online consultation form that asks about your health, current medicines (including flucloxacillin), and any conditions that might affect your suitability for ED treatment. A UK-registered prescriber will review your answers, usually within 24 hours, and if tadalafil is appropriate for you, your medicine will be dispensed by our pharmacy and delivered discreetly to your home.

We stock a range of tadalafil options to suit different needs and budgets, including generic tadalafil tablets and branded Cialis. All our ED medicines are genuine, UK-licensed products sourced from reputable manufacturers. If you have any questions about taking tadalafil with flucloxacillin or any other medicine, our pharmacists are available to help—simply contact us via the website or by phone.

Remember that erectile dysfunction can sometimes be an early warning sign of underlying health conditions such as heart disease, diabetes, or high blood pressure [1]. If you are experiencing ED for the first time, or if it has worsened recently, it is a good idea to see your GP for a check-up. Your GP can investigate possible causes, check your cardiovascular health, and refer you for specialist advice if needed. Treating ED with tadalafil is effective for many men, but it works best as part of a broader approach to your health and wellbeing.

What if tadalafil does not work for you?

If tadalafil does not work as well as you hoped, or if you experience side effects, do not give up. Other PDE5 inhibitors—such as sildenafil (Viagra), vardenafil (Levitra), or avanafil (Spedra)—may suit you better, as individuals respond differently to each medicine [3][5][6]. Your prescriber can discuss alternatives during a follow-up consultation. It is also worth reviewing lifestyle factors: stopping smoking, losing weight if needed, exercising regularly, reducing alcohol, and managing stress can all improve erectile function and make ED treatment more effective [2]. If oral medicines do not help, your GP can refer you to a specialist who may offer other treatments such as vacuum devices, alprostadil injections or cream, or psychological support if anxiety or relationship issues are contributing to your ED.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 21 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 21 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 21 October 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 21 October 2026]
5. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 21 October 2026]
6. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 21 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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