Tadalafil and Moxifloxacin: Can You Take Them Together?

Tadalafil and Moxifloxacin: Understanding the Interaction

Published: 23 October 2026

If you've been prescribed tadalafil and moxifloxacin, you may be wondering whether these medicines can be taken together safely. Tadalafil is a treatment for erectile dysfunction (ED), while moxifloxacin is a fluoroquinolone antibiotic used to treat bacterial infections. Although no major direct interaction between tadalafil and moxifloxacin is commonly reported in standard references, both medicines can affect your heart rhythm, so your prescriber will carefully review your individual circumstances before confirming that the combination is suitable for you.

What Is Tadalafil and How Does It Work?

Tadalafil is a prescription medicine used to treat erectile dysfunction 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 are sexually aroused [1]. This increased blood flow helps you achieve and maintain an erection suitable for sexual activity.

Tadalafil is available in two forms: 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 once a day) [4]. The medicine only works when you are sexually stimulated—it does not cause an automatic erection. Tadalafil is the active ingredient in branded Cialis and is also available as a generic medicine at Cured Pharmacy, following an online consultation reviewed by a UK prescriber.

What Is Moxifloxacin and When Is It Prescribed?

Moxifloxacin is a broad-spectrum antibiotic from the fluoroquinolone family, used to treat serious bacterial infections such as pneumonia, sinusitis, and certain skin infections. It works by stopping bacteria from multiplying and repairing themselves, helping your immune system to clear the infection. Moxifloxacin is usually prescribed when other antibiotics are not suitable or when the infection is caused by bacteria known to respond to fluoroquinolones.

Because moxifloxacin is a potent antibiotic, it is only available on prescription and is typically used for short courses (often 5 to 10 days). Like all fluoroquinolones, moxifloxacin carries important warnings: it can very rarely affect tendons (causing tendonitis or rupture), nerves, and heart rhythm. Your doctor will check your medical history carefully before prescribing it, especially if you have a history of heart rhythm problems, low potassium or magnesium levels, or if you are taking other medicines that can affect your heart's electrical activity.

Do Tadalafil and Moxifloxacin Interact?

There is no widely reported major direct drug interaction between tadalafil and moxifloxacin in standard UK references such as the British National Formulary [4]. However, both medicines can individually affect your cardiovascular system, which is why your prescriber will assess the combination carefully. Moxifloxacin is known to prolong the QT interval—a measure of the heart's electrical cycle seen on an ECG. A prolonged QT interval can, in rare cases, lead to a serious abnormal heart rhythm called torsades de pointes.

Tadalafil can lower blood pressure slightly and is contraindicated in people with certain serious heart conditions [4]. While tadalafil itself does not typically prolong the QT interval, taking it alongside another medicine that does (such as moxifloxacin) means your prescriber must review your overall heart health, current medicines, and any risk factors. If you have a history of heart rhythm problems, low electrolyte levels, or are taking other QT-prolonging medicines, your doctor may choose an alternative antibiotic or monitor you more closely.

What Happens in Your Body?

When you take moxifloxacin, it can slightly delay the repolarisation phase of your heart's electrical cycle, which is measured as the QT interval on an ECG. Tadalafil works mainly on blood vessels, helping them relax to improve blood flow. The concern is not that tadalafil directly worsens the QT effect, but that if your heart is already under strain or you have other risk factors, combining medicines that affect the cardiovascular system requires careful consideration. Your prescriber will check your full medication list, medical history, and any recent blood tests (such as potassium and magnesium levels) to ensure the combination is safe for you.

What Your Prescriber Checks Before Approving Tadalafil and Moxifloxacin Together

Before confirming that you can take tadalafil and moxifloxacin together, your prescriber will review several important factors. They will ask about your heart health, including any history of abnormal heart rhythms (arrhythmias), recent heart attack, stroke, or unstable angina. They will also check whether you are taking any other medicines that can prolong the QT interval or lower blood pressure, such as certain antidepressants, antipsychotics, or other antibiotics.

Your prescriber will review your current medicines to ensure you are not taking nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called poppers, as these are absolutely contraindicated with tadalafil and can cause a dangerous drop in blood pressure [4]. They will also check for medicines that affect how your body processes tadalafil, such as potent CYP3A4 inhibitors (including some antifungals and HIV medicines), which can raise tadalafil levels and require dose adjustments.

If you have low potassium or magnesium levels (which can increase the risk of QT prolongation), your doctor may want to correct these before starting moxifloxacin. They will also consider your age, kidney and liver function, and whether sexual activity is safe for you given your overall health. At Cured Pharmacy, every prescription for tadalafil is reviewed by a UK-registered prescriber following your online consultation, ensuring all interactions and contraindications are checked.

Practical Advice: Taking Tadalafil and Moxifloxacin Safely

If your prescriber has confirmed that you can take tadalafil and moxifloxacin together, follow their instructions carefully. Take each medicine exactly as prescribed—do not change the dose or stop either medicine without medical advice. Moxifloxacin is usually taken once a day, with or without food, and you should complete the full course even if you start to feel better, to ensure the infection is fully cleared.

Tadalafil can be taken on-demand (at least 30 minutes before sexual activity) or as a daily low dose, depending on your prescription [4]. Avoid drinking large amounts of alcohol while taking tadalafil, as this can increase the risk of dizziness and low blood pressure, and may make erectile dysfunction worse [1]. Grapefruit juice can raise tadalafil levels in your blood, so it is best avoided.

Be alert to warning signs that need urgent medical attention: if you experience chest pain, a very fast or irregular heartbeat, fainting, sudden severe dizziness, or an erection lasting more than four hours (priapism), seek immediate help by calling 999 or going to A&E. If you notice sudden loss of vision or hearing, stop taking tadalafil and contact a doctor straight away. If you develop severe tendon pain, swelling, or difficulty moving a joint while taking moxifloxacin, stop the antibiotic and see your GP urgently, as fluoroquinolones can rarely cause tendon damage.

When to Contact Your Doctor

Contact your GP or prescriber if you experience new or worsening side effects from either medicine, such as persistent headache, flushing, indigestion, back pain (common with tadalafil), or nausea, diarrhoea, or dizziness (which can occur with moxifloxacin). If you are prescribed any new medicine while taking tadalafil and moxifloxacin, tell the prescribing doctor or pharmacist about both medicines to avoid further interactions. Never take tadalafil with another PDE5 inhibitor (such as sildenafil or vardenafil) or with nitrates, nicorandil, riociguat, or poppers, as these combinations are dangerous [3][4].

Other Medicines and Tadalafil: What Else Should You Know?

Beyond moxifloxacin, tadalafil can interact with several other types of medicine. Alpha-blockers (such as doxazosin, tamsulosin, or alfuzosin), used for high blood pressure or prostate problems, can cause a significant drop in blood pressure when combined with tadalafil [4]. If you take an alpha-blocker, you should be stable on it before starting tadalafil, and your prescriber will usually start you on the lowest dose of the ED medicine.

Potent CYP3A4 inhibitors—including ritonavir, cobicistat (found in some HIV medicines), ketoconazole, itraconazole, and clarithromycin—can raise tadalafil levels in your blood, increasing the risk of side effects [4]. Your prescriber may reduce your tadalafil dose or choose a different ED treatment if you are taking one of these medicines. Conversely, CYP3A4 inducers such as rifampicin, carbamazepine, phenytoin, and St John's wort can make tadalafil less effective by speeding up how quickly your body breaks it down.

Other blood-pressure-lowering medicines (such as ACE inhibitors, calcium-channel blockers, or diuretics) can add to the blood-pressure-lowering effect of tadalafil, which is usually manageable but must be declared during your consultation [4]. Always tell your prescriber and pharmacist about every medicine you take, including over-the-counter products, herbal remedies, and supplements, so they can check for interactions and ensure your treatment is safe.

Erectile Dysfunction Treatments Available at Cured Pharmacy

Cured Pharmacy offers a range of licensed ED treatments following an online consultation reviewed by a UK prescriber. Options include generic sildenafil (from £0.45 per tablet, or £0.36 with first-order code Ednew), generic tadalafil (from £7.95, or £6.36 with code Ednew), vardenafil (£16.95, or £13.56 with code Ednew), and Spedra (avanafil, £20.95, or £16.76 with code Ednew). Branded Viagra and Cialis are also available. Your prescriber will recommend the most suitable treatment based on your health, preferences, and any interactions with your current medicines. All PDE5 inhibitors work in a similar way but differ in how quickly they start working and how long they last, so your prescriber can help you choose the best option for your lifestyle.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 23 October 2026]
2. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 23 October 2026]
3. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 23 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.