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 Take Mounjaro While Breastfeeding?
Mounjaro (tirzepatide) is not recommended while breastfeeding, and healthcare professionals advise against its use during nursing. Current evidence suggests tirzepatide may pass into breast milk, and the effects on breastfed infants are not fully understood. The UK prescribing information and NHS guidance both recommend that women should not breastfeed while taking Mounjaro. If you're considering weight management options while nursing, your GP can discuss safer alternatives and timing for potential future 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.
Why Mounjaro Is Not Recommended During Breastfeeding
Mounjaro is a prescription-only medicine that is contraindicated (not recommended) during breastfeeding. The active ingredient, tirzepatide, is not expected to remain in your system long-term, but because insufficient safety data exists specifically for breastfed infants, the precautionary principle applies.
The tirzepatide KwikPen prescribing information explicitly states that women should not breastfeed during treatment and for some time after discontinuing the medication. Additionally, Mounjaro works by affecting appetite regulation and glucose metabolism — systems that are still developing in infants. Until more robust safety data exists, healthcare professionals recommend waiting until breastfeeding has finished before starting treatment. If you're currently breastfeeding and interested in weight management support, your GP can provide personalised guidance based on your individual circumstances and discuss NHS-aligned alternatives.
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.
Safe Weight Management While Breastfeeding
If you're breastfeeding and seeking weight management support, evidence-based approaches focus on gradual, sustainable methods that are safe for nursing. Gentle dietary adjustments — increasing protein and fibre while maintaining adequate calories for milk production — can support modest weight loss without compromising lactation. Regular, moderate physical activity is also safe during breastfeeding and benefits overall health.
Your GP or a dietitian can provide personalised advice on safe calorie intake while nursing, typically 300–500 kcal above non-breastfeeding needs. Once breastfeeding has finished, prescription weight loss options like Mounjaro or Wegovy (semaglutide) may become available to you. Use our free BMI calculator to track your current weight and health metrics, and discuss your timeline and options with your healthcare provider.
- 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 tirzepatide safe in breast milk?
Current evidence suggests tirzepatide may pass into breast milk, but safety data for breastfed infants is insufficient. For this reason, prescribers recommend against use during breastfeeding as a precautionary measure until more research is available.
When can I start Mounjaro after stopping breastfeeding?
Once you've fully weaned your baby, you can discuss starting Mounjaro with your GP or prescriber. They'll assess your eligibility based on your BMI and health status. There's typically no waiting period after breastfeeding stops, but your prescriber will provide individual guidance.
What weight loss options are safe while breastfeeding?
Sustainable dietary changes, adequate protein intake, and moderate physical activity are safe during nursing. Avoid very low-calorie diets, as they can reduce milk supply. Your GP or dietitian can provide tailored advice to support gentle weight loss without compromising lactation.
Can I use Wegovy instead of Mounjaro while breastfeeding?
No. Wegovy (semaglutide) is also not recommended during breastfeeding for the same reasons as Mounjaro — insufficient safety data for breastfed infants. Both are GLP-1 medications and both carry the same contraindication.
How do I know when it's safe to consider prescription weight loss treatment?
Once breastfeeding has completely finished, discuss your weight management goals with your GP. They'll assess your BMI using our free BMI calculator, review your health history, and determine whether prescription options like Mounjaro or Wegovy are appropriate for you based on current NHS eligibility criteria.
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.