Tadalafil and Metronidazole: 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 [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 [1]. Unlike some other ED treatments, tadalafil has a longer duration of action – its effects can last up to 36 hours, which is why it's sometimes called 'the weekend pill' [4].

Tadalafil is available in two forms: on-demand tablets (10mg or 20mg) taken at least 30 minutes before sexual activity, and daily low-dose tablets (2.5mg or 5mg) taken once a day [4]. Both require sexual stimulation to work – tadalafil does not cause an automatic erection. At Cured Pharmacy, tadalafil is available from £7.95 after an online consultation with a UK prescriber, with first-order discounts available using code Ednew.

Common side effects include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. These are usually mild and temporary. Tadalafil is not suitable for everyone, particularly men taking nitrates, nicorandil, riociguat, or those for whom sexual activity is inadvisable due to heart conditions [4].

What is Metronidazole and When is it Prescribed?

Metronidazole is an antibiotic and antiprotozoal medicine used to treat a wide range of bacterial and parasitic infections. It is commonly prescribed for dental infections, bacterial vaginosis, pelvic inflammatory disease, infected leg ulcers, pressure sores, and certain gut infections. Metronidazole works by entering bacterial cells and disrupting their DNA, which stops the bacteria from growing and multiplying.

The medicine is available as tablets (usually 200mg, 400mg, or 500mg), suppositories, vaginal gel, and intravenous infusion for severe infections. A typical course might be 400mg taken two or three times daily for five to seven days, though your doctor will tailor the dose and duration to your specific infection. It's important to complete the full course even if you feel better, to ensure the infection is fully cleared.

Metronidazole is well-known for causing an unpleasant reaction if you drink alcohol while taking it – symptoms can include flushing, nausea, vomiting, headache, and rapid heartbeat. You should avoid alcohol during treatment and for at least 48 hours after finishing the course. Other common side effects include a metallic taste in the mouth, nausea, and darkening of the urine, which is harmless.

Why Might You Need Both Medicines?

You might be prescribed metronidazole for an infection while already taking tadalafil for erectile dysfunction, or vice versa. These are two completely different types of medicine treating unrelated conditions, so it's not unusual for them to be needed at the same time. The key is ensuring your prescriber knows about all your current medicines so they can check for any potential issues and adjust doses if necessary.

When to get urgent help

• Erection lasting longer than 4 hours (priapism) – go to A&E or call 999 immediately
• Sudden loss of vision in one or both eyes – stop tadalafil and seek urgent medical attention
• Chest pain during or after sexual activity – stop and seek help; do not take GTN if you've used tadalafil within 48 hours
• Sudden decrease or loss of hearing, sometimes with ringing in ears or dizziness – seek urgent medical advice
• Signs of severe allergic reaction (rash, swelling, difficulty breathing) to either medicine – call 999

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

Tadalafil and Metronidazole: Is There an Interaction?

No major interaction between tadalafil and metronidazole is commonly reported in standard drug interaction databases or clinical practice [3][4]. Metronidazole is not known to significantly affect the way tadalafil is broken down in the body, nor does tadalafil interfere with metronidazole's antibiotic action. This means that, in most cases, the two medicines can be taken together when both are needed.

However, 'no major interaction' does not mean the combination is automatically suitable for everyone. Your prescriber will still need to review your individual circumstances during your consultation. They will consider your overall health, other medicines you're taking, any existing medical conditions (particularly heart, liver, or kidney problems), and whether the infection you're treating might affect your ability to engage in sexual activity comfortably.

It's worth noting that feeling unwell with an infection can naturally reduce sexual desire and performance, regardless of medication. If you're taking metronidazole for an infection, you may find you're not interested in sexual activity until you've recovered. This is completely normal and doesn't mean the tadalafil isn't working – it simply reflects how your body prioritises healing when you're unwell.

Always inform your prescriber or pharmacist about every medicine you're taking, including antibiotics like metronidazole, even if you think there's no interaction. This allows them to provide personalised advice and ensure your treatment plan is safe and appropriate for you.

What Your Prescriber Checks Before Approving Tadalafil

When you request tadalafil through Cured Pharmacy's online consultation, a UK-registered prescriber will review your medical history and current medicines carefully [2]. They will specifically check for medicines that must never be taken with tadalafil, including nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, and recreational drugs called 'poppers' [3][4]. Taking tadalafil with any of these can cause a dangerous drop in blood pressure.

Your prescriber will also look for medicines that can interact with tadalafil in other ways. Alpha-blockers (such as tamsulosin or doxazosin, used for prostate problems or high blood pressure) can add to tadalafil's blood-pressure-lowering effect, causing dizziness [4]. If you take an alpha-blocker, you'll need to be stable on it and start tadalafil at the lowest dose. Potent CYP3A4 inhibitors – certain antifungals, some HIV medicines, and a few antibiotics like clarithromycin – can raise tadalafil levels in your blood, requiring dose adjustments [4].

The prescriber will ask about your heart health, blood pressure, liver and kidney function, any history of stroke or heart attack, and conditions affecting your eyes. Tadalafil is not suitable when sexual activity itself is inadvisable, such as after a recent heart attack or stroke, or if you have severe heart failure or very low blood pressure [2][4]. They'll also check whether ED might be a sign of an underlying condition like diabetes or cardiovascular disease that needs investigation by your GP [1][2].

Declaring All Your Medicines

It's essential to list every medicine you take during your consultation, including prescription medicines, over-the-counter treatments, herbal remedies, vitamins, and supplements. Even if you think something is unrelated to ED treatment, it might interact with tadalafil or provide important context for your prescriber. For example, St John's wort (a herbal remedy for low mood) can make tadalafil less effective, while grapefruit juice can raise its levels in your blood [4].

At a glance

Practical Advice for Taking Tadalafil and Metronidazole Together

If your prescriber approves both medicines, you can take them on the same day without needing to space them apart by a specific number of hours. Tadalafil can be taken with or without food, though a very heavy, high-fat meal might delay how quickly it starts working [4]. Metronidazole is usually taken with or after food to reduce the chance of stomach upset. Follow the instructions on each medicine's label and patient information leaflet.

Remember that metronidazole requires you to avoid alcohol completely during treatment and for at least 48 hours afterwards. This is important regardless of whether you're also taking tadalafil. Alcohol can make erectile dysfunction worse and adds to the blood-pressure-lowering effect of tadalafil, increasing the risk of dizziness or fainting [1][4]. Avoiding alcohol while you're on antibiotics also helps your body fight the infection more effectively.

If you feel unwell while taking metronidazole – which is common when you have an infection – it's perfectly fine to skip taking tadalafil until you feel better. Tadalafil is an on-demand treatment (or a daily low-dose option), not something you must take every day regardless of whether you plan sexual activity. Listen to your body and prioritise recovering from your infection first.

Keep both medicines in their original packaging, out of sight and reach of children, and store them according to the instructions (usually at room temperature, away from moisture). Check the expiry dates and never share your medicines with anyone else, even if they have similar symptoms. If you experience any unexpected side effects or feel concerned about taking the two medicines together, contact your pharmacist or prescriber for advice.

When to Seek Medical Help While Taking These Medicines

While tadalafil and metronidazole can usually be taken together safely, you should be aware of warning signs that need urgent medical attention. If you develop an erection that lasts longer than four hours (priapism), seek immediate help by going to A&E or calling 999 [4]. Priapism is a medical emergency that requires treatment to prevent permanent damage to the penis. It is rare but can occur with any ED medicine.

Sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing (sometimes with ringing in the ears or dizziness), requires immediate medical attention [4]. Stop taking tadalafil and seek urgent help. These are rare but serious side effects. If you experience chest pain during or after sexual activity, stop and seek medical help – do not take nitrate medicines (GTN spray) if you've taken tadalafil within the last 48 hours, as this combination is dangerous [4].

For metronidazole, seek medical advice if you develop severe or persistent diarrhoea, signs of an allergic reaction (rash, swelling, difficulty breathing), or unusual neurological symptoms such as numbness, tingling, seizures, or confusion. If your infection symptoms worsen or don't improve after a few days of treatment, contact your prescriber. These signs might indicate the antibiotic isn't working or that you need a different treatment approach.

Less urgent side effects – such as headache, indigestion, back pain from tadalafil, or nausea and metallic taste from metronidazole – are common and usually manageable [4]. If they're troublesome or persistent, speak to your pharmacist for advice. They can suggest ways to reduce discomfort or discuss whether a different dose or medicine might suit you better.

Ongoing Support from Cured Pharmacy

After your prescription is approved and dispensed, Cured Pharmacy's team remains available to answer questions about your medicines. If you're unsure about anything – whether it's how to take your tablets, managing side effects, or checking a new medicine your GP has prescribed – you can contact the pharmacy for advice. Your safety and confidence in your treatment are the priority.

In summary

• No major interaction between tadalafil and metronidazole is commonly reported in clinical practice
• Your prescriber reviews all your medicines during consultation to ensure the combination is safe for you
• Avoid alcohol completely while taking metronidazole and for 48 hours after finishing the course
• Feeling unwell with an infection may naturally reduce sexual interest until you recover
• Seek urgent help for erection lasting over 4 hours, sudden vision loss, or chest pain during sex

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