Tadalafil and Erythromycin: Can They Be Taken Together?

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What is tadalafil and how does it work?

Tadalafil is a prescription medicine licensed in the UK to treat erectile dysfunction (ED) [4]. 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. Unlike some other ED treatments, tadalafil does not cause an erection on its own—sexual stimulation is still needed for it to work [4].

Tadalafil is available in two forms: on-demand tablets (usually 10 mg or 20 mg, taken at least 30 minutes before sexual activity) and daily low-dose tablets (2.5 mg or 5 mg, taken once a day at the same time). The on-demand dose can remain effective for up to 36 hours, which is why tadalafil is sometimes called the 'weekend pill' [4]. All forms require a prescription in the UK, and treatment is only supplied after an online or face-to-face consultation with a registered prescriber who will review your medical history and current medicines.

Common side effects include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. Serious side effects are rare but include prolonged erections lasting more than four hours (priapism), sudden vision or hearing loss, and chest pain during sex. Tadalafil is not suitable for everyone, particularly men taking nitrates, nicorandil, riociguat, or those for whom sexual activity is not advisable due to heart conditions [4].

What is erythromycin and why is it prescribed?

Erythromycin is a macrolide antibiotic used to treat a range of bacterial infections, including chest infections (such as pneumonia and bronchitis), skin infections (such as acne and cellulitis), ear infections, and sexually transmitted infections like chlamydia [12]. It works by stopping bacteria from making the proteins they need to grow and multiply, helping your immune system clear the infection.

Erythromycin is usually taken as tablets or capsules, typically two to four times a day, depending on the infection being treated. A typical course lasts between five and fourteen days. It is often prescribed for people who are allergic to penicillin antibiotics. Common side effects include nausea, vomiting, diarrhoea, stomach cramps, and loss of appetite [12].

Erythromycin is also known to interact with several other medicines because it affects the way the liver breaks down drugs. Specifically, it inhibits an enzyme called CYP3A4, which is responsible for metabolising many medicines, including tadalafil [12]. This means that when you take erythromycin alongside tadalafil, the level of tadalafil in your blood can rise, potentially increasing the risk of side effects. Understanding this interaction is important for safe use of both medicines.

How do tadalafil and erythromycin interact?

Tadalafil and erythromycin interact because erythromycin is a moderate-to-strong inhibitor of the liver enzyme CYP3A4, which is responsible for breaking down tadalafil in the body [4][12]. When erythromycin slows this process, tadalafil stays in your bloodstream for longer and at higher concentrations than usual. This can increase the likelihood and severity of side effects such as headache, dizziness, flushing, low blood pressure, and visual disturbances.

The interaction is pharmacokinetic, meaning it affects how your body processes tadalafil rather than how tadalafil works at its site of action. The British National Formulary notes that the maximum recommended dose of tadalafil should be reduced when taken with potent CYP3A4 inhibitors [4]. Erythromycin is generally considered a moderate inhibitor, but caution is still advised, particularly if you are taking higher doses of tadalafil or have other risk factors such as liver or kidney problems.

This does not mean you cannot take tadalafil and erythromycin together, but it does mean your prescriber will need to adjust your dose or timing, and you should be vigilant for side effects. The interaction is well-recognised and manageable with appropriate medical oversight. Never adjust your dose yourself or take tadalafil without declaring that you are on erythromycin—your prescriber must know about all your current medicines to make a safe decision [4][12].

Why CYP3A4 matters for drug interactions

CYP3A4 is one of the most important enzymes in the liver for drug metabolism, responsible for breaking down around half of all medicines in common use. When a medicine like erythromycin inhibits CYP3A4, it can cause other drugs that rely on this enzyme—such as tadalafil—to build up in the body. This is why prescribers always ask about antibiotics, antifungals, and other medicines that affect CYP3A4 before approving ED treatment. Other common CYP3A4 inhibitors include clarithromycin (another macrolide antibiotic), ketoconazole and itraconazole (antifungal medicines), and some HIV medicines like ritonavir [4]. If you are taking any of these, your prescriber will adjust your tadalafil dose or consider an alternative ED treatment.

What you need to know

• Erythromycin raises tadalafil levels in your blood, increasing the risk of side effects.
• Your prescriber will usually lower your tadalafil dose if you are taking erythromycin.
• Declare all antibiotics and medicines during your consultation for safe treatment.
• The interaction is manageable with medical oversight; do not adjust doses yourself.
• Alternative ED treatments are available if the interaction poses too great a risk.

What will my prescriber check before approving tadalafil?

Before prescribing tadalafil, your clinician will review your full medical history and all current medicines, including over-the-counter products, herbal supplements, and any antibiotics such as erythromycin [2][4]. They will specifically check for contraindications—medicines or conditions that make tadalafil unsafe. These include nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, and recreational drugs called 'poppers' (amyl or alkyl nitrites). Taking tadalafil with any of these can cause a dangerous drop in blood pressure and is strictly contraindicated [4].

Your prescriber will also assess your cardiovascular health, as sexual activity places demands on the heart. Tadalafil is not suitable if you have had a recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or if your doctor has advised against sexual activity [2][4]. If you take medicines for high blood pressure or an enlarged prostate (alpha-blockers such as doxazosin or tamsulosin), your prescriber will ensure you are stable on these before starting tadalafil at the lowest effective dose.

When erythromycin is part of your current treatment, your prescriber will typically recommend a lower starting dose of tadalafil or advise waiting until you have finished the antibiotic course, depending on the urgency of your ED treatment and your overall risk profile. They may also discuss alternative ED medicines if the interaction poses too great a risk. Honesty during your consultation is essential—never withhold information about antibiotics or other medicines, as this could put your health at risk [4][12].

Declaring all your medicines: why it matters

Many men worry about listing every medicine during a consultation, but this step is critical for your safety. Drug interactions are one of the most common preventable causes of adverse effects, and your prescriber cannot protect you if they do not have the full picture. This includes prescription medicines, over-the-counter painkillers, herbal remedies like St John's wort (which can reduce tadalafil's effectiveness), and recreational drugs. If you are unsure whether something counts as a 'medicine', declare it anyway—your prescriber would much rather hear about something irrelevant than miss a dangerous interaction [2][4].

Practical advice if you are taking both medicines

If your prescriber has approved tadalafil while you are taking erythromycin, follow their dosing instructions exactly. You will likely be prescribed a lower dose than usual—for example, 10 mg instead of 20 mg for on-demand use, or a reduced frequency if you are on daily tadalafil [4]. Do not take extra tablets or adjust the timing yourself, even if you feel the effect is weaker than expected. The interaction means tadalafil will stay in your system longer, so increasing the dose could lead to a build-up and increase the risk of side effects.

Be particularly alert for side effects such as dizziness, headache, flushing, visual changes (such as a blue tinge to vision or increased sensitivity to light), or a drop in blood pressure when standing up quickly. If you experience chest pain during or after sexual activity, stop immediately and seek urgent medical help—do not take more tadalafil [4]. Avoid drinking large amounts of alcohol, as this can worsen low blood pressure and make ED worse. Grapefruit juice can also raise tadalafil levels and should be avoided while taking both medicines [4].

If you develop severe or persistent side effects, contact your prescriber or GP. Do not simply stop taking erythromycin without medical advice, as this could allow your infection to return or become resistant to treatment. Similarly, do not stop tadalafil abruptly if it was prescribed for daily use—speak to your clinician first. Once you finish your course of erythromycin, the interaction will gradually resolve as the antibiotic leaves your system, usually within a few days. Your prescriber may then adjust your tadalafil dose back to the standard level if appropriate [4][12].

When to get urgent help

• Erection lasting more than 4 hours (priapism) – go to A&E immediately
• Sudden loss of vision or hearing – stop tadalafil and seek urgent medical help
• Chest pain during or after sexual activity – stop, rest, and call 999 if pain does not resolve
• Severe dizziness or fainting – sit or lie down and contact your GP or call 111
• Allergic reaction (rash, swelling, difficulty breathing) – call 999 immediately

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

Are there alternative ED treatments if the interaction is a concern?

If the interaction between tadalafil and erythromycin poses too great a risk, or if you prefer to avoid it altogether, your prescriber can discuss alternative ED treatments. Other PDE5 inhibitors—such as sildenafil (Viagra), vardenafil (Levitra), and avanafil (Spedra)—are also affected by CYP3A4 inhibitors, but to varying degrees [3][5][6]. Sildenafil may be used with caution at a lower starting dose, while vardenafil and avanafil are generally avoided or contraindicated with potent CYP3A4 inhibitors [5][6]. Your prescriber will review the Summary of Product Characteristics (SmPC) for each medicine to determine the safest option for you.

Non-oral treatments may also be considered. Eroxon is a topical gel that works locally and does not interact with antibiotics or other systemic medicines, making it a safe alternative during a course of erythromycin. Vitaros (alprostadil cream) and Caverject (alprostadil injection) are prescription-only options that work by a different mechanism and are not affected by CYP3A4 inhibitors [7]. These treatments may be suitable if you have not responded to PDE5 inhibitors or if drug interactions make oral ED medicines unsuitable.

In some cases, the simplest solution is to wait until you have completed your antibiotic course before starting or resuming tadalafil. Erythromycin is usually prescribed for five to fourteen days, and the interaction risk diminishes once the antibiotic has cleared your system [12]. If your ED is not urgent, this approach avoids the need for dose adjustments and reduces the risk of side effects. Your prescriber will help you weigh the benefits and risks of each option based on your individual circumstances [2][4].

When to see your GP about erectile dysfunction

If you are experiencing ED for the first time, it is important to see your GP for a full assessment before seeking treatment online. ED can be an early warning sign of underlying health conditions such as cardiovascular disease, diabetes, high blood pressure, or hormonal imbalances [1][2]. Your GP can arrange blood tests, check your heart health, review your medicines, and refer you to a specialist if needed. Treating ED without addressing the underlying cause may mean missing an opportunity to improve your overall health. Online consultations are convenient and appropriate for many men, but they are not a substitute for a thorough medical review if ED is new, worsening, or accompanied by other symptoms [1][2].