The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro and Getting Pregnant — What You Need to Know
If you're considering getting pregnant or planning to conceive, stopping Mounjaro before pregnancy is strongly recommended. Mounjaro (tirzepatide) is a prescription-only weight management injection that has not been tested in pregnancy, so the risks to a developing baby are unknown. Your GP or prescriber should be involved in planning your pregnancy and advising when to stop treatment. This guide explains the key information about Mounjaro, fertility, and conception planning in the UK context.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Mounjaro and Pregnancy — Key Safety Information
Mounjaro must be stopped before trying to get pregnant. Clinical trials have not studied tirzepatide in pregnant women, so the safety for a developing baby cannot be confirmed. The UK Patient Information Leaflet and prescribing guidance state that Mounjaro is not recommended during pregnancy.
When to stop: If you are planning to conceive, discuss with your GP or prescriber about stopping Mounjaro. Generally, it is recommended to stop at least 3 months before trying to get pregnant to allow the medication to clear from your body, though your prescriber may advise differently based on your individual circumstances.
Fertility and conception: Mounjaro does not affect fertility in men or women. However, gradual weight management can sometimes affect menstrual cycles in women, which may impact conception timing. If your periods become irregular during Mounjaro treatment, mention this to your GP.
Breastfeeding: Mounjaro should not be used while breastfeeding, as it is not known whether tirzepatide passes into breast milk.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Planning Pregnancy While on Weight Management Treatment
If you are overweight or obese and planning to conceive, achieving a healthier weight before pregnancy can improve fertility outcomes and reduce pregnancy complications. Mounjaro can support weight loss whilst you are not trying to conceive — but stopping before conception is essential. Discuss a timeline with your GP: you may want to stop Mounjaro now if actively trying to conceive, or continue briefly if pregnancy is planned further ahead.
After stopping, focus on sustainable lifestyle changes — balanced diet, physical activity, and stress management — to maintain weight loss during pregnancy planning and early pregnancy. Your GP can refer you to a dietitian or weight management support if needed. Using our free BMI calculator can help you track whether you're in a healthier weight range for conception and pregnancy.
What About Other Weight Loss Medications?Wegovy (semaglutide) is also contraindicated in pregnancy and should be stopped before trying to conceive — similar guidance applies. Saxenda (liraglutide), another GLP-1 injection, also cannot be used during pregnancy. All prescription weight loss injections are pregnancy-category C medications, meaning animal studies have shown effects on the fetus, but human studies are lacking.
If you are currently taking any weight loss injection — whether Mounjaro, Wegovy, or another GLP-1 medication — speak to your prescriber urgently if you discover you are pregnant. Do not continue the injection, but do not suddenly stop other medications (like diabetes treatments) without guidance. Your GP will advise on safe next steps and may refer you to maternity services for specialist input.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Can I get pregnant while taking Mounjaro?
Mounjaro has not been tested in pregnant women, so pregnancy is not recommended whilst taking it. If you become pregnant whilst on Mounjaro, stop the injection immediately and inform your GP. Your healthcare team will provide specialist pregnancy care.
How long before getting pregnant should I stop Mounjaro?
Discuss this with your prescriber — stopping at least 3 months before trying to conceive is often recommended to allow the medication to clear your system. Some prescribers may advise stopping sooner if you are actively trying. Individual circumstances vary.
Does Mounjaro affect fertility or the ability to get pregnant?
Mounjaro does not directly affect fertility in men or women. However, gradual weight management can sometimes cause irregular periods, which may affect conception timing. Achieving a healthier weight before pregnancy generally improves fertility and pregnancy outcomes.
What if I'm breastfeeding — can I take Mounjaro?
No, Mounjaro is not recommended during breastfeeding because it is unknown whether tirzepatide passes into breast milk. If you want to resume weight management after pregnancy, speak to your GP — there may be alternatives once breastfeeding is complete.
Is it safe to use Wegovy instead of Mounjaro if I'm trying to get pregnant?
No. Wegovy (semaglutide), like Mounjaro, must be stopped before conception because it has not been tested in pregnancy. All GLP-1 and GIP/GLP-1 weight loss injections should be stopped before trying to get pregnant — discuss timing with your prescriber.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.