Mounjaro and antibiotics: what you should know

Yes, most antibiotics can be taken alongside Mounjaro.

Antibiotics are not listed as a contraindication (something not to be used) in the Mounjaro patient information leaflet. There are no direct drug interactions listed between tirzepatide – the active ingredient in Mounjaro – and commonly prescribed antibiotics.

However, both Mounjaro and antibiotics can sometimes cause side effects like nausea, vomiting, or diarrhoea, particularly when treatment starts. If these symptoms are significant, they can affect how well oral medicines are tolerated or absorbed, making antibiotics less efficient.

Antibiotics do not stop Mounjaro from working. However, feeling unwell can make taking tablets more difficult, which is why symptom management matters.

Delayed gastric emptying

Mounjaro slows gastric emptying (the speed your stomach empties) as part of how it reduces appetite and supports weight loss.

For most people, this does not usually affect how antibiotics are absorbed and does not require dose changes. However, it can influence how comfortable tablets feel to take.

If you already feel nauseous or have a reduced appetite, tablets may feel harder to tolerate, particularly early in treatment or during dose increases.

Vomiting and diarrhoea

Nausea, vomiting and diarrhoea are all common side effects of Mounjaro, affecting more than 1 in 10 people. Many antibiotics can also cause gastrointestinal upset. For example, amoxicillin and flucloxacillin list symptoms including vomiting and diarrhoea as common side effects.

Taking two medicines that can upset the stomach at the same time increases the chance that symptoms may feel more noticeable or harder to manage.

This matters because vomiting or ongoing diarrhoea can make it difficult to keep antibiotic doses down. It can also increase the risk of dehydration - which is particularly concerning if you are already unwell with an infection.

➤ If symptoms are mild, treatment can often continue. If symptoms are persistent or severe, medical advice is important.

Dehydration

Mounjaro can sometimes indirectly cause dehydration due to the common gastrointestinal side effects like vomiting and diarrhoea, which can lower fluid intake or increase fluid loss.

Infections themselves – and antibiotics that may cause diarrhoea – can further increase the risk of dehydration.

Dehydration can make you feel more unwell, and slow your recovery from infection, so it is important to pay attention to fluid intake if symptoms occur.

➤ There is no clear evidence that Mounjaro can affect your menstrual cycle, though some people taking it notice changes to their periods.

Mounjaro is taken once weekly and can usually be continued as normal while you are taking antibiotics, unless a doctor specifically advises otherwise.

There is no need to change the timing of your Mounjaro injection to fit around antibiotics. The focus should be on how you feel, rather than exact timing.

If you start to feel sick (nausea), vomit or have diarrhoea, you should:

• sip fluids regularly to reduce the risk of dehydration
• eat small, light meals if you can tolerate food
• take antibiotics exactly as prescribed and do not double doses if you are sick
• seek advice (from a pharmacist, your GP or by calling 111) if you vomit soon after taking an antibiotic dose or cannot keep tablets down

You should seek medical advice urgently if:

• you cannot keep antibiotics or fluids down
• vomiting or diarrhoea lasts longer than 24 hours
• you notice signs of dehydration, such as dizziness, a dry mouth, dark urine, or passing urine less often
• you have severe, persistent abdominal pain
• your infection symptoms are not improving or are getting worse

Mounjaro has relatively few direct drug interactions, but there are some medications to be aware of:

1. Diabetes medicines – Using Mounjaro alongside insulin or sulfonylureas can increase the risk of low blood sugar, so doses may need review.
2. Oral medicines – Because Mounjaro slows gastric emptying, tablets may feel harder to tolerate if you’re nauseous, but this rarely requires dose changes.
3. Contraceptive pills – Mounjaro may affect how contraceptive pills work, it is advised to use extra protection when starting Mounjaro or after any dose increase. Vomiting or severe diarrhoea can reduce absorption of oral contraception. Extra protection is advised during these episodes.
4. Other interacting drugs – Some antibiotics, such as clarithromycin, interact with many common medicines. This is not specific to Mounjaro, but highlights the importance of a full medication check when starting antibiotics.

Asda Online Doctor offers Mounjaro and other weight loss treatments as part of a safe, medically-reviewed service.

When prescribing treatments, our online doctors take into account your medical history, current medicines, and any conditions that could affect safety - including whether you’re taking antibiotics or other treatments.

If you’re unsure whether Mounjaro is right for you, or if you have concerns about side effects or interactions, a doctor can help you decide on the most appropriate option.