Mounjaro Pregnancy Side Effects: What UK Patients Need to Know (October 2026)

01 · The short answer

What happens if you get pregnant on Mounjaro?

You stop the medicine and speak to your prescriber promptly. The UK prescribing information is clear: Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive.¹ If you become pregnant during treatment, stop the medicine and tell your prescriber promptly.¹³

Do not take another dose while you wait for an appointment. Contact the prescribing team, or your GP or midwife, and say exactly which dose you were on and when you last injected.

02 · Your next step

Which situation are you in?

Your next step depends on whether you are planning a baby, might already be pregnant, or simply want to avoid pregnancy while treated.

03 · Side effects in pregnancy

Mounjaro side effects and pregnancy

The honest answer is that Mounjaro is not meant to be used in pregnancy, so there is no safe "pregnancy dose" and no list of acceptable side effects to manage. The instruction is to stop the medicine and tell your prescriber promptly.¹

For more on the topic, see our guides to Mounjaro pregnancy safety and risks and the first week after a positive test.

04 · Usual side effects

The usual Mounjaro side effects, and why they matter here

Like all medicines, Mounjaro can cause side effects, and most are digestive.¹ Nausea, diarrhoea, vomiting, constipation and abdominal discomfort are the most common. Dizziness, reduced appetite, reflux and hair shedding are also common.

This creates a practical problem. Early pregnancy can bring its own nausea and tiredness, so the two can look alike. If your period is late, or you have had unprotected sex, do a test rather than assuming your symptoms are down to the pen. Most Mounjaro side effects appear in the first days after starting or increasing a dose, peak early and settle as your body adapts.¹ Symptoms that are new, unexpected or not following that pattern deserve a conversation with your prescriber.

Our guides to gastro side effects of Mounjaro, potential side effects and rare side effects go through the full picture. If nausea or vomiting is persistent or you cannot keep fluids down, contact your clinical team — dehydration needs prompt attention.

05 · Contraception and fertility

Contraception, fertility and unplanned pregnancy

The pill is the method to think about, because Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are 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 This applies to the pill only; implants, coils and injections are unaffected.

Plan for that from the start rather than after a missed period.

For women with PCOS, weight loss is a first-line recommendation that can improve insulin resistance, cycles and symptoms, and improving weight can restore ovulation.¹ Mention PCOS and any fertility plans in your consultation.

06 · Stopping and clearance

How long Mounjaro stays in your system

Tirzepatide 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 There is no way to speed this up, and nothing needs doing while it clears.

That clearance period sits alongside the instruction to stop at least one month before trying to conceive. In practice, if you are planning a baby, tell your prescriber early so you can agree a stop date and keep reliable contraception in place until you are ready. Do not rely on the pill alone around dose changes.

07 · Mood, hormones and reporting

Hormonal changes, mood and reporting a problem

Tell your prescriber about any new symptom.

Regulators have looked at mood. The EMA's safety committee reviewed the evidence and concluded in 2024 that it does not support a causal link between GLP-1 medicines and suicidal thoughts, and the MHRA keeps this under continuous review.¹⁷ Pregnancy, or a pregnancy scare, is stressful in itself, so seek help promptly if your mood drops or you have distressing thoughts. Our guide to psychological side effects covers this further.

If you have thoughts of harming yourself or ending your life, get help straight away. Call 999 or go to A&E if you are in immediate danger. In England you can call NHS 111 and choose the mental health option, any time. You can also call Samaritans free on 116 123, day or night. Tell your prescriber about any change in your mood while taking Mounjaro.

If you took Mounjaro and later found you were pregnant, you can report it through the MHRA Yellow Card scheme.¹⁹ See also Mounjaro reported side effects.

08 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help 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 skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. 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.¹

09 · NHS and private routes

NHS and private access when planning a family

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the primary-care rollout began in June 2025 with the highest-need groups first.⁴ Our NHS pregnancy guide explains how this interacts with family planning.

Tell your prescriber about contraception, fertility plans and breastfeeding. Current prescribing information indicates minimal transfer of tirzepatide into breast milk, but discuss it with your prescriber so the decision reflects your circumstances.¹

Mounjaro is a prescription-only medicine used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.