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
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Supplements for Weight Loss and Muscle Gain in the UK
Many people search for supplements to support weight loss and muscle gain, but the evidence for most over-the-counter products is limited. If you're looking for clinically-proven support for weight management in the UK, prescription weight loss medications may be an option. This guide covers what's actually available through the NHS and private prescribing, who's eligible, and how to find out if prescription weight loss treatment could help you. We'll also explain how these options compare to traditional supplements.
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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 Prescription Weight Loss Options
If you're interested in weight management with stronger clinical evidence, the UK offers several prescription-only medications that have been licensed specifically for weight loss and muscle preservation. These include:
- Mounjaro (tirzepatide) — a once-weekly injection that works through two hormone pathways (GIP and GLP-1 agonist). In clinical trials, Mounjaro helped participants lose an average of 15–21% of their body weight when combined with diet and exercise.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical trials showed average weight loss of approximately 15% of body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection, typically resulting in modest weight loss support.
These medications are available through NHS specialist weight management services or private online prescribing following a clinical assessment. Unlike supplements, they are prescription-only and require a qualified prescriber to assess your suitability. Calculate your personal BMI using our free calculator to see whether you might fall within the eligibility criteria, and explore potential weight loss outcomes with our GLP-1 weight loss calculator.
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 and How to Get Started
In the UK, access to prescription weight loss medication varies depending on whether you pursue the NHS or private route. Through the NHS, you'll typically be referred to a tier 3 specialist weight management service by your GP—though waiting lists can be lengthy in many areas, and availability depends on your local health system. Private prescribing is faster: you complete an online consultation with a UK-licensed prescriber, and if suitable, you receive a prescription dispensed by a GPhC-registered pharmacy.
Eligibility generally requires a BMI of 30 or above, or 27 or above if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can discuss which route and medication might suit your circumstances. Start by having a conversation with your practice about nhs weight loss options available to you, or explore private prescribing through accredited providers. Track your progress with our free progress tracker once you begin any weight management programme.
- 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.
Are weight loss supplements regulated in the UK?
Most over-the-counter weight loss supplements are food supplements, not medicines, and face less stringent regulation than pharmaceuticals. Claims must be evidence-based, but efficacy is often modest. Prescription medications like Mounjaro and Wegovy undergo rigorous MHRA testing and have proven clinical trial data behind them, making them a more evidence-backed option for eligible adults seeking weight management.
Will prescription weight loss medication help me gain muscle?
Prescription weight loss medications like Mounjaro and Wegovy work primarily by reducing appetite and supporting fat loss, not directly building muscle. However, they can help create the calorie deficit needed for weight loss while you maintain or increase protein intake and exercise, which supports muscle preservation during weight loss. Combine medication with strength training for best results.
How do I know if I'm eligible for prescription weight loss treatment in the UK?
Generally, you're eligible if your BMI is 30 or above, or 27 or above with a weight-related health condition. Your GP can assess this and refer you to NHS specialist services, or you can complete a private online consultation. Use our free BMI calculator to check your current BMI and discuss eligibility with your healthcare provider.
What's the difference between GLP-1 medications and weight loss supplements?
GLP-1 medications (like Wegovy) and dual GIP/GLP-1 medications (like Mounjaro) are prescription pharmaceuticals with proven clinical trial efficacy—typically 15–21% average weight loss. Most supplements lack this level of evidence. Prescription options require clinical assessment and monitoring, whereas supplements are self-managed. Your GP can advise which approach suits you.
How quickly will I see results with prescription weight loss medication?
Weight loss typically begins within 2–4 weeks, with most progress seen between weeks 8 and 16 as your dose increases. Average weight loss is 15–21% of body weight over 6–12 months, though individual results vary significantly. Sustainable results require combining medication with a reduced-calorie diet and increased physical activity. Track your progress with our free tracker.
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.