Tadalafil and Rifaximin: Can You Take Them Together?

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What is tadalafil and how does it work?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men. 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're sexually aroused [4]. Tadalafil does not cause an erection on its own—sexual stimulation is still needed for it to work.

In the UK, tadalafil is available as generic tablets or under the brand name Cialis. It comes in two main forms: on-demand tablets (10mg or 20mg) taken at least 30 minutes before sex, with effects lasting up to 36 hours, and daily tablets (2.5mg or 5mg) taken once a day at the same time [4]. The long duration of the on-demand dose is why tadalafil is sometimes called the 'weekend pill'.

Tadalafil is broken down in your liver by an enzyme system called CYP3A4. This is important because some medicines can speed up or slow down this process, potentially affecting how well tadalafil works or increasing the risk of side effects. Your prescriber will check for these interactions during your consultation to ensure tadalafil is safe and effective for you.

What is rifaximin and why is it prescribed?

Rifaximin is a prescription antibiotic that works mainly in your gut. Unlike most antibiotics, very little rifaximin is absorbed into your bloodstream—it stays in your digestive system, where it kills bacteria causing infection or inflammation. In the UK, rifaximin is most commonly prescribed for traveller's diarrhoea caused by certain bacteria, or to reduce episodes of hepatic encephalopathy (a complication of severe liver disease).

Because rifaximin acts locally in the gut and only tiny amounts enter your bloodstream, it has fewer interactions with other medicines compared to antibiotics that are fully absorbed. It is usually taken as a tablet two or three times a day for a short course, depending on the condition being treated.

Rifaximin belongs to the rifamycin family of antibiotics, which includes rifampicin—a medicine known to interact with many drugs. However, rifaximin behaves very differently because of its minimal absorption. This is why rifaximin does not typically cause the same drug interactions as rifampicin, but your prescriber will still review your full medication list to be certain.

When to get urgent help

• Erection lasting more than four hours (priapism)
• Sudden loss of vision in one or both eyes
• Sudden hearing loss or ringing in the ears
• Chest pain during sex (do not take nitrates if you have used tadalafil in the past 48 hours)
• Severe allergic reaction such as swelling of the face, lips, or throat, or difficulty breathing

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

Can you take tadalafil and rifaximin together?

There is no commonly reported major interaction between tadalafil and rifaximin. Because rifaximin is poorly absorbed from the gut into the bloodstream, it does not significantly affect the liver enzymes (CYP3A4) that break down tadalafil [4]. This means rifaximin is unlikely to change how tadalafil works or increase your risk of side effects.

It is important to distinguish rifaximin from rifampicin, a related antibiotic that is fully absorbed and is a potent CYP3A4 inducer. Rifampicin can make tadalafil less effective by speeding up its breakdown in the liver. Rifaximin does not have this effect, so the two medicines can generally be taken together without dose adjustment.

That said, every person's situation is different. During your online consultation at Cured Pharmacy, the prescriber will review all your current medicines, including rifaximin, to check for any individual factors that might affect your treatment. You should always declare every medicine you take—prescription, over-the-counter, or herbal—so the prescriber can make a fully informed decision about your safety.

What your prescriber checks

When you request tadalafil through Cured Pharmacy, a UK-registered prescriber reviews your medical questionnaire before approving your treatment. They will check for contraindications such as use of nitrates, nicorandil, riociguat, or another PDE5 inhibitor, all of which must never be taken with tadalafil. They will also look at your blood pressure, heart health, and any other medicines you take, including rifaximin, to ensure tadalafil is safe and appropriate for you [2][4].

Tadalafil and rifaximin: what it means in practice

If you are taking rifaximin and your prescriber approves tadalafil, you can usually take both medicines as directed without needing to adjust the dose or timing of either. Rifaximin is typically taken with or without food, and tadalafil can also be taken with or without food, so there is no special timing required between the two.

Continue taking rifaximin exactly as your doctor prescribed—do not stop or change the dose without advice, even if you start tadalafil. If you are taking tadalafil on-demand (10mg or 20mg), take it at least 30 minutes before you plan to have sex; if you are on the daily dose (2.5mg or 5mg), take it at the same time each day. Sexual stimulation is still needed for tadalafil to work [4].

Be aware of the common side effects of each medicine. Tadalafil can cause headache, indigestion, back pain, muscle aches, flushing, or a stuffy nose. Rifaximin may cause nausea, constipation, or dizziness. If you experience any new or worsening symptoms after starting both medicines together, contact your GP or pharmacist for advice. Serious side effects are rare but require urgent help—see the warning signs section below.

Medicines that do interact with tadalafil

While tadalafil and rifaximin can generally be taken together, there are some medicines that must never be combined with tadalafil because they can cause a dangerous drop in blood pressure. These include nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, and recreational drugs called 'poppers' (amyl or alkyl nitrites). Do not take tadalafil if you use any of these [4].

Alpha-blockers (such as doxazosin, tamsulosin, alfuzosin, or terazosin) are used for high blood pressure or prostate problems and can also lower blood pressure when combined with tadalafil. If you take an alpha-blocker, your prescriber will usually start you on the lowest dose of tadalafil and ensure you are stable on the alpha-blocker first [4].

Potent CYP3A4 inhibitors—such as ritonavir, cobicistat (found in some HIV medicines), Paxlovid (used for COVID-19), ketoconazole, itraconazole, or clarithromycin—can raise tadalafil levels in your blood and increase the risk of side effects. Your prescriber may need to reduce your tadalafil dose or choose a different ED treatment if you take any of these medicines [4]. Always declare your full medication list during your consultation.

Grapefruit juice and alcohol

Grapefruit juice can increase the amount of tadalafil in your bloodstream, potentially raising the risk of side effects such as headache or low blood pressure. It is best to avoid grapefruit juice while taking tadalafil. Heavy alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect of tadalafil, so drink in moderation [4].

When to seek medical advice about tadalafil and rifaximin

If you develop any unexpected symptoms after starting tadalafil while taking rifaximin, contact your GP or pharmacist. While serious interactions are not expected between these two medicines, individual responses can vary. Common side effects of tadalafil—such as headache, flushing, or indigestion—are usually mild and go away on their own, but if they are severe or persistent, seek advice [4].

Seek urgent medical help if you experience an erection lasting more than four hours (priapism), sudden loss of vision in one or both eyes, sudden hearing loss or ringing in the ears, or chest pain during sex. These are rare but serious side effects that need immediate attention. If you have chest pain, do not take nitrates (such as GTN spray) if you have used tadalafil in the past 48 hours, as this combination is dangerous [4].

If you are prescribed a new medicine while taking tadalafil, always tell the prescriber or pharmacist that you are using tadalafil for erectile dysfunction. Similarly, if your rifaximin course finishes and you are prescribed a different antibiotic or any new treatment, declare your tadalafil use so your healthcare team can check for interactions. Never stop a prescribed medicine without professional advice.

Getting tadalafil at Cured Pharmacy

Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering discreet, convenient access to ED treatments. All prescription medicines, including tadalafil, are only supplied after an online consultation reviewed by a UK-registered prescriber. You can choose from a range of tadalafil options, including generic tablets from £7.95 (£6.36 with first-order code Ednew) and branded Cialis from £12.00 (£9.60 with code Ednew). Your treatment is delivered in plain, discreet packaging.

In summary

• No major interaction is commonly reported between tadalafil and rifaximin
• Rifaximin is poorly absorbed and does not affect how tadalafil works
• Your prescriber reviews all your medicines during consultation to confirm safety
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers
• Seek urgent help for erections over four hours or sudden vision or hearing loss

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