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
Shakes and Weight Loss — Prescription Options in the UK
While meal replacement shakes can support a reduced-calorie diet, prescription weight loss medication may be available for eligible adults in the UK. If you're interested in weight management through medication, several prescription weight loss options are licensed in the UK, alongside lifestyle changes. This guide explains how GLP-1 weight loss medications work, who may be eligible, and how to access them through the NHS or private prescribing. Calculate your BMI using our free calculator above to check if you may qualify for prescription support.
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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-Licensed Weight Loss Medications
Three prescription-only medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are injectable medications given once weekly, whilst Saxenda is a daily injection.
- Mounjaro: Dual GIP and GLP-1 receptor agonist. Clinical trials showed average weight loss of 15–21% of body weight at the highest dose.
- Wegovy: GLP-1 receptor agonist. Evidence suggests average weight loss of approximately 15% of body weight.
- Saxenda: GLP-1 receptor agonist given daily. Average weight loss approximately 5–10% of body weight.
All three are prescription-only and require a clinical assessment to determine suitability. Individual results vary significantly.
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.
Eligibility and How to Access Weight Loss Medication
In the UK, adults may be eligible for weight loss medication if they have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease. Lower BMI thresholds apply to people of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS access: Referral to a tier 3 specialist weight management service is typically required, though availability and waiting times vary by region. Private access: GPhC-registered online pharmacies offer prescription weight loss medication following an online clinical assessment, with no NHS referral needed. Speak with your GP to discuss which option is right for you, or use our weight loss calculator to explore potential outcomes.
- 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 I use shakes alongside prescription weight loss medication?
Yes. Prescription weight loss medications are designed to be used alongside a reduced-calorie diet and increased physical activity. Meal replacement shakes can form part of a calorie-controlled diet plan. Always discuss your diet plan with your prescriber or a healthcare professional to ensure it's balanced and safe.
What's the difference between Mounjaro and Wegovy?
Mounjaro contains tirzepatide (dual GIP and GLP-1 agonist) and Wegovy contains semaglutide (GLP-1 agonist only). In clinical trials, Mounjaro showed slightly higher average weight loss (15–21% vs 15%), though individual results vary. Both are prescription-only and require a clinical assessment.
How long does it take to see weight loss results with medication?
Results typically become noticeable after 4–8 weeks of treatment at therapeutic doses. The medications work gradually, and doses are increased slowly over several weeks. Most significant weight loss occurs between weeks 8 and 20. Consistency with diet and exercise is essential.
Is weight loss medication available on the NHS?
Yes, Mounjaro and Wegovy are available through NHS specialist weight management services (tier 3). Access requires referral from your GP and varies significantly by region. Waiting times can be lengthy in some areas. Private prescribing offers faster access without NHS referral.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain. These typically improve over time. Rare serious side effects can include pancreatitis symptoms (severe stomach pain) or gallbladder problems. Always report new or persistent side effects to your prescriber.
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.