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
Is Mounjaro Safe When Breastfeeding?
Mounjaro (tirzepatide) is not recommended for use while breastfeeding, according to current UK prescribing information and NHS guidance. If you're breastfeeding and considering weight management support, your GP or healthcare provider can discuss safer alternatives and the timing of any treatment. This guide explains the medical reasoning, what the evidence shows, and what options are available to you in the UK.
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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 contraindicated (not recommended) during breastfeeding because there is insufficient evidence that tirzepatide is safe for breastfed infants. While the full pharmacological impact on breast milk composition is not completely understood, the precautionary principle means that healthcare providers in the UK advise against its use.
The UK prescribing information for Mounjaro explicitly states that women who are breastfeeding should not use this medication. This is a category of absolute contraindication — similar to pregnancy — because the potential risks to the nursing infant cannot be ruled out with current evidence. If you're breastfeeding and managing your weight, speak with your GP about evidence-based alternatives such as structured diet support, physical activity programmes, or behavioural interventions through NHS weight management services.
Clinically BackedWeight Loss
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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.
When You Can Consider Mounjaro After Breastfeeding
If you've finished breastfeeding and are considering tirzepatide or other GLP-1 weight loss medications, your GP or a specialist can assess your eligibility. In the UK, access to Mounjaro is through NHS tier 3 specialist weight management services or private prescribing following a clinical assessment. You'll need a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes or high blood pressure.
The timing of stopping breastfeeding and starting Mounjaro is a clinical decision best made with your healthcare provider, taking into account your individual health and family circumstances.
If you're currently breastfeeding and interested in weight loss support, NHS tier 1 services offer free behavioural support, digital tools, and community weight management programmes that are safe during breastfeeding. These evidence-based approaches support sustainable weight loss without medication. You can also use our free BMI calculator to track your current health metrics and discuss them with your GP, who can signpost you to local weight management services while you're nursing.
- 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 tirzepatide pass into breast milk?
It is not known whether tirzepatide passes into breast milk. Due to this uncertainty, UK prescribing guidance recommends avoiding Mounjaro entirely during breastfeeding as a precautionary measure. Your GP can discuss what is known and answer specific questions about your situation.
How long after stopping breastfeeding can I take Mounjaro?
There is no specific waiting period mandated in UK guidance. However, your GP or specialist will assess your readiness for prescription weight loss treatment based on your overall health, BMI, and any weight-related conditions. Discuss timing with your healthcare provider at your assessment.
Are there safe weight loss options while breastfeeding in the UK?
Yes. NHS tier 1 weight management services offer free support including behavioural programmes, physical activity guidance, and dietary advice that are safe during breastfeeding. These evidence-based approaches support healthy weight loss without medication.
What if I become pregnant while taking Mounjaro?
Mounjaro is contraindicated in pregnancy. If you plan to become pregnant or think you might be, inform your prescriber immediately. You should use reliable contraception while taking tirzepatide and for 4 weeks after stopping, as recommended in UK guidance.
Can I use other weight loss injections like Wegovy while breastfeeding?
No. Wegovy (semaglutide) and all other GLP-1 receptor agonist medications are also contraindicated during breastfeeding due to insufficient safety data. Always discuss any weight loss treatment plans with your GP before starting, especially if you're nursing.
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.