Can You Take Nitrofurantoin With Mounjaro? (October 2026)

01 · The core answer

Can you take nitrofurantoin with Mounjaro?

This is a question for a prescriber or pharmacist who can see your full medicines list.

Mounjaro (tirzepatide) activates GIP and GLP-1 receptors, and one effect is that it slows how quickly the stomach empties.¹ Anything swallowed as a tablet or capsule passes through the same stomach. That is why every prescriber and pharmacist wants to know you are using it before they add something new.

If you have been prescribed nitrofurantoin for a urinary infection, you do not need to panic and you do not need to wait. You do need to make sure the person prescribing and the person dispensing both know about your weekly injection.

02 · Your next step

What to do if you have been prescribed it

Start by telling the prescriber you use Mounjaro, and name the strength you are currently on. Tell the pharmacist again when you collect the antibiotic, even if you think it was already noted. Records are not always shared between services, so a second mention costs nothing.

Then read the patient leaflet that comes in the antibiotic box, and the Mounjaro patient information leaflet if you want to compare. Finish the course exactly as your prescriber and the label instruct. Do not shorten it because you feel better, and do not extend it on your own.

Keep your weekly Mounjaro schedule unless a clinician tells you otherwise. If you cannot keep fluids down, contact your clinical team — dehydration needs medical help straight away.

03 · Why mention it

Why a short conversation is worth having

Antibiotics are only useful if they are absorbed and taken as directed. A medicine that changes stomach emptying is exactly the kind of detail a pharmacist wants to hear about. In most cases the conversation will be brief and reassuring. Occasionally it leads to practical advice about timing or what to do if you are unwell.

If something feels different after starting the antibiotic, note when it began and what you ate and drank. That detail makes it far easier for a clinician to work out what is going on.

04 · How Mounjaro works

How Mounjaro works and why it matters for other medicines

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes. It comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹

Tirzepatide activates two natural gut-hormone receptors at once: GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin. In practice, most people feel fuller sooner and less hungry between meals.¹

The slower stomach emptying is the feature that links Mounjaro to almost every question about taking tablets, capsules and liquids alongside it. It does not mean other medicines stop working. It means the people looking after you should know.

Tirzepatide also has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system.¹ That is worth remembering: the medicine is still present for weeks after you stop, so telling a prescriber you recently stopped is just as relevant as telling them you are currently on it.

05 · Antibiotics and your pharmacist

Antibiotics in general while on Mounjaro

Nitrofurantoin is only one of several antibiotics a person might be given. The same principle applies to all of them: tell the prescriber you use Mounjaro, and ask the pharmacist to check your medicines list.

If you see a page claiming a specific antibiotic is completely safe or completely forbidden with Mounjaro, treat it with caution. A reliable answer depends on your kidneys, your other medicines, allergies, pregnancy status and the infection itself. A web page cannot see those.

Read the Mounjaro SmPC and the patient leaflet. The leaflet for the antibiotic is the equivalent document on the other side. Between them, plus a pharmacist, you have a trustworthy picture.

Readers often ask similar questions about other everyday medicines. We have pages on taking acyclovir alongside Mounjaro and using Nurofen on Mounjaro, which follow the same cautious approach.

06 · Stomach side effects

When stomach upset has more than one possible cause

Antibiotics and GLP-1 medicines can both affect how your digestion feels. That makes it harder to tell what is causing a symptom.

A practical approach is to keep a short note. Write down the day you started the antibiotic, the day of your most recent Mounjaro injection, and when any symptom began or changed. Bring that note to your pharmacist or prescriber.

If a symptom is severe, persistent or frightening, do not wait for a scheduled review; contact a prescriber, NHS 111 or your GP. For severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of the skin or eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing, seek immediate medical help.

Any new symptom that you think could be linked to a medicine can be reported through the Yellow Card scheme.¹⁹ Reports from patients help regulators spot patterns.

Heartburn or indigestion remedies are another common add-on during an illness. See our pages on Rennie with Mounjaro and Rennies on Mounjaro for how we handle that question.

07 · Other medicines to mention

Other medicines worth mentioning to your prescriber

Whenever a new medicine is added, give the prescriber the full list: prescription medicines, over-the-counter products, vitamins and herbal or traditional remedies. Gaps in the list are the most common reason an interaction check is incomplete.

Some categories deserve a specific mention. If you take oral contraceptives, note that Mounjaro slows stomach emptying, which can reduce how well the pill is absorbed.⁷ The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion); your prescriber may need to adjust those medicines.

Supplements are often forgotten. Products such as shilajit and Zapain are examples of things people take without thinking of them as medicines. Mention them anyway.

08 · Getting the UTI treated

Getting a urinary infection assessed

A suspected urinary infection should be assessed by a GP, an NHS urgent service or a community pharmacy that offers a consultation. Antibiotics are prescription-only, so you cannot simply buy them. Be cautious of any website offering to supply them without a consultation or prescription.

Describe your symptoms, mention any previous infections and any allergies, and say you use Mounjaro. If you are pregnant, may be pregnant or have known kidney problems, say so at the start. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly.

Fever, back or side pain, blood in the urine, or feeling very unwell are reasons to be seen urgently rather than waiting for a routine appointment. Recurrent infections deserve a proper review with a clinician too.

Fluids and rest matter during any infection, particularly if your appetite is already lower on treatment. If you cannot eat or drink normally, tell your prescriber so they can advise on your Mounjaro dose and the antibiotic together.

09 · Staying on track with treatment

Staying on track with Mounjaro during an illness

A short illness does not usually mean the end of your progress, but decisions about missing or delaying a dose belong to your prescriber. Do not double up or improvise. Contact the prescribing team and follow what they say.

Our aftercare includes ongoing monthly reviews, dose titration and follow-up assessments by the prescribing team, plus side-effect support. If you are one of our patients and you start a new medicine, tell us. Support is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, through the account portal chat or by phone on 0333 207 0413.

Mounjaro is a prescription-only medicine supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.

10 · Where to check reliable information

Where to check reliable information

For interactions, check the product information for each medicine and ask a pharmacist. The SmPC is the professional document and the patient information leaflet is its plain-language companion.¹¹³