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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Best Weight Loss Supplements in the UK: Prescription Options
When searching for the best weight loss supplements in the UK, it's important to understand that prescription medications are the most evidence-based option available for weight management. If you're looking for effective support, prescription weight loss injections like Mounjaro and Wegovy are licensed in the UK and may help eligible adults lose weight alongside lifestyle changes. These are different from over-the-counter supplements — they require a clinical assessment and prescription from a licensed healthcare professional. Use our free BMI calculator above to check your starting point, then explore whether prescription weight management might be right for you.
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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 Medications
The most effective prescription weight management options available in the UK include Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are GLP-1 receptor agonist medications — different from traditional diet supplements — that work by helping regulate appetite and supporting fuller feelings after meals.
- Mounjaro: Once-weekly injection with a dual GIP and GLP-1 mechanism. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks at maximum dose.
- Wegovy: Once-weekly GLP-1 injection. STEP trials demonstrated approximately 14.9% average weight loss at the maximum 2.4mg dose.
- Saxenda: Daily GLP-1 injection, the oldest option. Evidence supports around 5–clinically studied weight loss in clinical studies.
All three are prescription-only medications requiring a clinical assessment before being prescribed. Individual results vary significantly based on lifestyle changes, genetics, and adherence.
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 in the UK
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Caribbean heritage, the NHS recommends lower thresholds — eligibility may start at BMI 27.5 or above.
Access in the UK comes through two routes: NHS specialist weight management services (via GP referral to tier 3/4 services, though waiting lists vary significantly by region) or private online prescribing through GPhC-registered pharmacies following a clinical assessment. Try our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, then discuss options with your GP.
- 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.
What's the difference between weight loss supplements and prescription medications?
Over-the-counter supplements have limited clinical evidence and are not regulated as medicines. Prescription weight loss medications like Mounjaro and Wegovy are licensed, clinically tested, and require a prescription. They work through specific biological mechanisms (GLP-1 receptor activation) and have proven efficacy in clinical trials. Always consult your GP about which option suits your health needs.
Can I get Mounjaro or Wegovy on the NHS in the UK?
Yes — both Mounjaro and Wegovy are available through NHS specialist weight management services (tier 3 and 4). Access is via GP referral, though availability and waiting times vary significantly by region and ICB funding. Your GP can discuss NHS eligibility and refer you if appropriate. Private prescribing is also available without NHS referral through registered pharmacies.
How much weight can I expect to lose with prescription weight loss medication?
Clinical trials show average losses of 15–21% of body weight with Mounjaro and around 15% with Wegovy over 72 weeks, alongside reduced-calorie diet and increased physical activity. However, individual results vary significantly — some people lose more, some less. Use our weight loss calculator to see projected ranges for different doses based on starting weight and other factors.
Are there side effects with prescription weight loss injections?
Yes — common side effects include nausea, diarrhoea, constipation, and stomach pain, particularly during dose increases. Most improve over time. Serious side effects are rare but can include pancreatitis or gallbladder issues. A prescriber will assess risks versus benefits during your clinical assessment. Always report unusual symptoms to your GP or healthcare provider immediately.
What's the best weight loss supplement for me specifically?
This depends on your BMI, health conditions, medical history, current medications, and personal preferences. A GP or licensed prescriber can assess your individual situation and discuss whether prescription medication is appropriate. You cannot self-diagnose or choose a medication alone — eligibility and suitability require professional clinical assessment. Speak to your GP today about your weight management options.
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.