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
What Is The Best Weight Loss Supplement in the UK?
When it comes to weight management in the UK, "supplements" often refer to prescription weight loss medications rather than over-the-counter pills. The most effective prescription options are GLP-1 receptor agonist injections—Mounjaro and Wegovy—which are licensed for weight management and available through NHS specialist services or private prescription. This guide explains what's actually available, how they work, and whether you might be eligible for prescription weight loss medication through your GP.
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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 Explained
Three main prescription medications are licensed in the UK for weight management:
- Mounjaro (tirzepatide): A once-weekly injection that works on two hormone pathways (GIP and GLP-1). Clinical trials showed users lost an average of 15–21% of their body weight over 72 weeks, though individual results vary.
- Wegovy (semaglutide): A once-weekly GLP-1 injection with similar effectiveness—around 15% average weight loss in clinical trials. Both are prescription-only and require a clinical assessment before being prescribed.
- Saxenda (liraglutide): A daily GLP-1 injection, less commonly used than weekly options but still available through NHS weight loss programmes and private prescription.
These are not dietary supplements in the traditional sense—they are prescription medicines that work alongside reduced-calorie diet and increased physical activity. You cannot buy them over the counter. Your eligibility depends on your BMI and health circumstances. Use our free BMI calculator to check where you stand, and our GLP-1 weight loss calculator can help estimate potential outcomes at different doses.
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 Eligibility
In the UK, weight management medication access depends on your BMI and health profile. NHS access is through tier 3 specialist weight loss services—you'll need a GP referral, though waiting lists vary significantly by region. Private access is available through UK-licensed online prescribers following an online assessment, without NHS referral.
You may be eligible if: Your BMI is 30 or above, or 27–29.9 with a weight-related condition like type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (from 27.5) due to higher health risks. Speak to your GP first—they can assess eligibility, discuss options, and make referrals. Track your progress with our free progress tracker once you begin any weight loss plan.
- 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 better than diet and exercise alone?
Prescription weight loss medications like Mounjaro and Wegovy are designed to work alongside diet and exercise changes, not replace them. Clinical trials show the best results come from combining medication with a reduced-calorie diet and increased physical activity. They may help you feel fuller longer and reduce cravings, making lifestyle changes easier to sustain.
Can I buy weight loss injections over the counter in the UK?
No. Mounjaro, Wegovy, and Saxenda are all prescription-only medicines in the UK. You cannot buy them without a prescription from a UK-licensed prescriber. Access is either through the NHS (via specialist services) or private prescription following an online clinical assessment with a registered healthcare provider.
How much weight will I lose on Mounjaro or Wegovy?
Individual results vary significantly. Clinical trials showed average weight loss of around 15–21% of body weight with Mounjaro and approximately 15% with Wegovy over several months. Some people lose more, others less. Weight loss depends on your starting weight, diet adherence, activity level, genetics, and how well you respond to the medication.
What's the difference between a weight loss supplement and weight loss medication?
Most "weight loss supplements" lack strong clinical evidence. Prescription medications like Mounjaro and Wegovy are rigorously tested, licensed by the MHRA, and approved for weight management. They work through specific biological pathways. Over-the-counter supplements are not regulated the same way and are generally less effective than prescription options.
Should I speak to my GP about weight loss medication?
Yes. Your GP can assess your BMI, discuss your health history, check if you have any weight-related conditions, and determine if you're eligible for NHS or private weight loss medication. They can also monitor your progress and manage any side effects. This conversation is the first step toward accessing the right support for you.
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.