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 I Get Pregnant While Taking Mounjaro?
No, Mounjaro is not recommended during pregnancy. If you're taking Mounjaro (tirzepatide) and planning to become pregnant, you should speak to your GP or prescriber before stopping. Mounjaro has not been adequately studied in pregnant women, and it may affect how oral contraceptives work. The MHRA advises that women of childbearing age should use reliable contraception whilst taking Mounjaro and continue it for 4 weeks after stopping the medication.
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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 the Evidence Shows
Mounjaro is contraindicated in pregnancy. The prescribing information states that Mounjaro should not be used during pregnancy, and women of childbearing potential must use effective contraception. Unlike some diabetes medications, tirzepatide has not been tested in pregnant women, so its safety cannot be assured. Animal studies have shown potential effects on foetal development, though this does not always translate to humans.
If you become pregnant whilst taking Mounjaro, you should contact your GP or prescriber immediately. They will advise whether to stop the medication. Do not stop Mounjaro suddenly without medical guidance, as abrupt cessation may affect your blood sugar control if you have type 2 diabetes.
- Mounjaro is not licensed for use during pregnancy
- Animal studies suggest potential risks to foetal development
- Human pregnancy data is unavailable
- Seek immediate medical advice if pregnancy occurs
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.
Contraception and Mounjaro — MHRA Guidance
The MHRA advises that Mounjaro may reduce the effectiveness of oral contraceptives (the combined pill, progestogen-only pill, and other hormonal methods that work via oral absorption). This is because Mounjaro slows gastric emptying, which can reduce how quickly oral medications are absorbed in the gut.
If you're taking Mounjaro and use an oral contraceptive, the MHRA recommends adding a barrier method (condoms) or switching to a non-oral method (injection, implant, coil, patch) for 4 weeks after starting Mounjaro AND 4 weeks after each dose increase. More reliable options include the IUD, implant, or injectable contraceptives, which are not affected by Mounjaro's gastric effects.
- 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 during pregnancy?
No. Mounjaro is contraindicated in pregnancy and has not been studied in pregnant women. Animal studies suggest potential foetal effects. If you become pregnant whilst taking Mounjaro, contact your GP immediately. Do not stop the medication without medical advice.
Does Mounjaro affect contraceptive pills?
Yes. Mounjaro may reduce the absorption of oral contraceptives, making them less effective. If taking a pill, add condoms or switch to a non-oral method (implant, coil, injection, patch) for 4 weeks after starting Mounjaro and after each dose increase.
Can I plan pregnancy while on Mounjaro?
If you're planning pregnancy, discuss this with your GP or prescriber before starting Mounjaro. You will need to stop the medication before trying to conceive. Your prescriber can advise on timing and any alternative treatments suitable for pregnancy.
What contraception is safest with Mounjaro?
Non-oral methods are safest with Mounjaro: the IUD (copper or hormonal), implant, injection, or patch. These are not affected by reduced gastric absorption. Avoid relying solely on oral contraceptives without barrier protection whilst taking Mounjaro.
What if I become pregnant accidentally on Mounjaro?
Contact your GP or prescriber immediately. Do not stop Mounjaro suddenly without guidance. Your healthcare team will assess your individual situation and advise whether to continue, adjust, or stop the medication based on your health and pregnancy stage.
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.