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
Free tracker included with every download this week
Pregnancy and Mounjaro — What You Need to Know
Mounjaro (tirzepatide) is not recommended during pregnancy in the UK. If you're taking this prescription weight management injection and planning to become pregnant, or if you've discovered you're pregnant whilst on treatment, you should contact your GP or prescriber immediately. This guide explains NHS guidance, what to do, and how to manage your weight safely during pregnancy.
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Calculate Your BMI Instantly
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.
Why Mounjaro Isn't Safe in Pregnancy
Mounjaro is contraindicated in pregnancy — meaning it should not be used during pregnancy. Here's why:
- Animal studies have shown reproductive toxicity at higher doses of tirzepatide, though human pregnancy data is extremely limited
- The medication affects gut hormone pathways critical to fetal development
- gradual weight management during pregnancy poses risks to the developing baby and can increase miscarriage risk
- Nausea, vomiting, and appetite suppression caused by Mounjaro increase the risk of malnutrition during the crucial first and third trimesters
The UK MHRA (Medicines and Healthcare products Regulatory Agency) and NHS guidance clearly state Mounjaro must be stopped before pregnancy. Your GP or specialist prescriber should have discussed contraception with you when starting this medication.
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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.
What to Do If You're Pregnant or Planning Conception
If you're planning to become pregnant, tell your prescriber now — do not stop Mounjaro suddenly without guidance. Your prescriber will create a safe plan, which typically involves stopping the injection and allowing it to clear from your body (approximately 2–3 weeks after your last dose).
If you've discovered you're pregnant whilst taking Mounjaro, contact your GP or the clinic that prescribed it immediately. Early medical advice is important. Do not continue the medication. Your GP can discuss safe weight management during pregnancy, which may include dietary advice, gentle activity, and close monitoring.
Weight loss medications are not appropriate during pregnancy — focus shifts to supporting healthy fetal development rather than maternal weight loss.
If you've discovered you're pregnant whilst taking Mounjaro, contact your GP or the clinic that prescribed it immediately. Early medical advice is important. Do not continue the medication. Your GP can discuss safe weight management during pregnancy, which may include dietary advice, gentle activity, and close monitoring.
Weight loss medications are not appropriate during pregnancy — focus shifts to supporting healthy fetal development rather than maternal weight loss. The NHS recommends that women with obesity who are pregnant receive specialist care from tier 3 weight management services alongside midwifery to ensure safe monitoring.
- 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 take Mounjaro while pregnant?
No. Mounjaro is contraindicated in pregnancy due to potential reproductive toxicity shown in animal studies and risks from gradual weight management and nutritional deficiency. UK guidance clearly advises against use during pregnancy. If you're pregnant or planning conception, contact your GP immediately.
What should I do if I become pregnant while on Mounjaro?
Stop taking Mounjaro and contact your GP or prescriber immediately. Do not continue injections. Early medical advice is important to ensure your safety and your baby's wellbeing. Your GP can discuss safe weight management during pregnancy.
If I want to get pregnant, when should I stop Mounjaro?
Tell your prescriber before stopping — do not stop suddenly without guidance. Typically, Mounjaro is discontinued at least 2–3 weeks before attempting conception to allow the medication to clear your body. Your prescriber will guide the timing based on your cycle.
Can I breastfeed while taking Mounjaro?
No. Mounjaro is not recommended during breastfeeding. It's unclear whether tirzepatide passes into breast milk, and safety data in nursing infants is lacking. If you're breastfeeding or planning to, discuss alternative weight management with your GP.
Is the Mounjaro KwikPen ever safe in pregnancy?
No. Regardless of the dose in the KwikPen device, Mounjaro (tirzepatide) at any dose is not safe during pregnancy or breastfeeding. Pregnancy is a contraindication to all doses. Your GP or NHS specialist team can discuss safe post-pregnancy management.
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.