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
Can You Get Pregnant On Mounjaro?
No, you should not become pregnant while taking Mounjaro (tirzepatide). The medication is not recommended during pregnancy due to limited safety data. If you're a woman of childbearing age considering Mounjaro treatment, it's essential to understand contraception requirements and when it's safe to conceive. This guide covers UK safety guidance, what your prescriber will advise, and how to plan fertility safely around weight management treatment.
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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.
Mounjaro and Pregnancy — What You Need to Know
Mounjaro is not recommended during pregnancy. The prescribing information states that women of childbearing age must use effective contraception whilst taking the medication and for at least 4 weeks after their final dose. This is a precautionary measure because safety data in pregnancy is limited.
If you're planning to become pregnant, discuss this with your prescriber before starting Mounjaro. You'll need to stop the medication before trying to conceive. The tirzepatide dose titration process typically takes several weeks to reach maintenance, so it's important to plan ahead.
- Do not use Mounjaro if you are pregnant or planning pregnancy
- Use effective contraception during treatment
- Continue contraception for 4 weeks after your final injection
- Discuss fertility plans with your GP or weight management prescriber
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
UK Prescribing Requirements and Contraception Guidance
When you're prescribed Mounjaro through either NHS specialist weight management services or private consultation, your prescriber will ask about your contraception and family planning. Women on Mounjaro must use reliable contraception methods, particularly if taking oral contraceptives—the medication may reduce how well birth control pills are absorbed.
If you're using oral contraceptives whilst on Mounjaro, your prescriber will recommend switching to a barrier method or non-oral contraceptive for 4 weeks after starting the medication and for 4 weeks following each dose increase. If you wish to try for a baby, plan this conversation with your prescriber well in advance so you can gradually stop treatment safely and allow the medication to clear from your system before attempting pregnancy.
- 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.
Is Mounjaro safe if I become pregnant accidentally?
No. If you discover you're pregnant whilst taking Mounjaro, stop the medication immediately and contact your GP or prescriber. Although limited data suggests tirzepatide is unlikely to cause major harm, pregnancy is not a recommended use. Your healthcare team will advise you on next steps and monitoring.
How long after stopping Mounjaro can I try to get pregnant?
After your final injection, wait at least 4 weeks before trying to conceive. This allows the medication to clear from your system. However, discuss specific timing with your prescriber—they may recommend longer depending on your individual circumstances and health history.
Can I use the Mounjaro KwikPen if I'm breastfeeding?
No. Mounjaro is not recommended during breastfeeding because it's unknown whether tirzepatide passes into breast milk. If you're breastfeeding or planning to breastfeed, discuss alternative weight management options with your GP.
What contraception should I use while on Mounjaro?
Effective contraception is essential. If using oral contraceptives, your prescriber will recommend switching to barrier methods or non-oral contraceptives (like the implant, injection, or coil) for 4 weeks during treatment and after dose increases, as Mounjaro may reduce oral contraceptive absorption.
Can I get Mounjaro on the NHS if I'm planning pregnancy?
Discuss your fertility plans with your GP before referral to an NHS specialist weight management service. If you're planning to conceive in the near future, your team may recommend alternative weight management strategies. Mounjaro is designed for longer-term use, so timing is important.
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.