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
Weight Loss and Breast Changes — What You Need to Know
When you lose weight, changes to breast tissue are common and entirely normal. Weight loss affects fat distribution across your body, and because breast tissue contains significant fat, breasts often change in size and shape during a weight loss journey. This guide explains what happens during weight loss and explores prescription weight loss options available through the NHS and private providers in the UK for eligible adults seeking sustainable, medically supported weight management.
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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.
UK Prescription Weight Loss Options
If you're considering weight loss medication, several prescription options are available in the UK for eligible adults. Mounjaro (tirzepatide) is a once-weekly injection that activates dual GLP-1 and GIP pathways, helping regulate appetite and support weight management alongside diet and exercise. Wegovy (semaglutide) is another once-weekly GLP-1 injection option, while Saxenda (liraglutide) is a daily injection. Clinical trials show these medications may help achieve an average weight loss of 15–21% of body weight, though individual results vary significantly.
- Mounjaro: starting dose 2.5 mg, maximum 15 mg weekly
- Wegovy: starting dose 0.25 mg, maximum 2.4 mg weekly
- Saxenda: starting dose 0.6 mg, maximum 3 mg daily
All three are prescription-only and require a clinical assessment to determine eligibility. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check where you currently fall on NHS weight ranges.
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.
NHS vs Private Access — How to Get Started
NHS access: Prescription weight loss medications are available through tier 3 specialist weight management services. You'll need a referral from your GP, though availability and waiting times vary significantly by region. Private access: UK-licensed online prescribers offer these medications following an online clinical assessment, with no NHS referral needed.
To find out if you're eligible, check your BMI using our free BMI calculator on this page. Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease) may be eligible. Start by speaking with your GP about your weight loss goals and medical options available to you.
- 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.
Why do breasts change when you lose weight?
Breast tissue contains fat, and when you lose weight, fat is drawn from throughout your body, including the breasts. This is why breast size often decreases during weight loss. The degree of change varies based on genetics, the amount of weight lost, and individual body composition. This is a normal, healthy part of the weight loss process.
Can prescription weight loss medication help me lose weight safely?
Yes. Medications like Mounjaro, Wegovy, and Saxenda are prescription-only and licensed in the UK for weight management in eligible adults. They work alongside diet and exercise, not instead of them. Clinical trials show they can help achieve significant weight loss when used with lifestyle changes. A prescriber will assess your individual suitability.
How do I know if I'm eligible for prescription weight loss treatment in the UK?
Eligibility depends on your BMI and health history. Adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions, may qualify. Use our free BMI calculator to check your current BMI. Your GP or a licensed prescriber can assess whether medication is appropriate for your individual circumstances.
What's the difference between NHS and private weight loss medication?
Both offer the same licensed medications (Mounjaro, Wegovy, Saxenda), but NHS access is through specialist services with a GP referral and potential waiting lists, while private services offer faster access following an online assessment. Costs, availability, and timelines differ by region and provider.
How much weight can I expect to lose with prescription weight loss injections?
Clinical trials show average weight loss of 15–21% of body weight over 68–72 weeks, depending on the medication and dose. However, individual results vary significantly based on your starting weight, adherence to diet and exercise, and personal metabolism. Your prescriber can give you a realistic picture for your situation.
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.