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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Weight Loss Supplements in the UK — What You Need to Know
Weight loss supplements in the UK range from over-the-counter products to prescription-only medications. The most effective options backed by clinical evidence are prescription weight loss injections like GLP-1 medications, which require assessment by a healthcare professional. This guide explains the different types of weight management supplements available, how they work, and what the NHS recommends for sustainable weight loss alongside lifestyle changes.
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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.
Prescription Weight Loss Medications — The Evidence
The most clinically proven weight loss supplements available in the UK are prescription-only GLP-1 receptor agonist medications. These include Wegovy (semaglutide) and Mounjaro (tirzepatide), both licensed by the MHRA for weight management in UK adults.
Wegovy is a once-weekly injection that activates the GLP-1 hormone pathway, helping reduce appetite and food cravings. In clinical trials (STEP-1), participants taking Wegovy lost an average of approximately 15% of their body weight alongside a reduced-calorie diet and increased physical activity. Mounjaro uses a dual GIP and GLP-1 mechanism and showed average weight loss of 15–21% in SURMOUNT trials.
Both medications:
- Are prescription-only — require clinical assessment before being prescribed
- Work best combined with diet and exercise, not as standalone treatments
- May be available through NHS specialist weight management services or private prescription
- Require ongoing medical monitoring
Individual results vary significantly based on adherence, lifestyle, and personal metabolism.
Clinically BackedWeight Loss
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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.
Over-the-Counter Weight Loss Supplements — Important Context
The UK market includes numerous over-the-counter weight loss supplements including caffeine-based products, fibre supplements, and herbal formulas. However, evidence for most OTC supplements is limited compared to prescription medications. The NHS emphasises that sustainable weight loss comes primarily from achieving a calorie deficit through diet and physical activity rather than supplements alone.
OTC products may support weight loss efforts as part of a comprehensive approach but should not replace lifestyle changes. Always check ingredient labels, look for reputable brands, and discuss any supplement with your GP before starting—especially if you take other medications or have existing health conditions. Our free BMI calculator can help you determine your current health category, while our weight loss projection calculator shows potential outcomes with different approaches.
- 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 Wegovy and Ozempic for weight loss?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2mg) and using it for weight loss is off-label. Wegovy is specifically licensed in the UK for weight management at higher doses (up to 2.4mg). Ask your prescriber about the licensed option appropriate for you.
Can I get weight loss supplements on the NHS?
GLP-1 medications like Wegovy and Mounjaro are available through NHS specialist tier 3 weight management services for eligible adults. Access varies by region and involves referral from your GP. Private prescription options are also available through registered online services.
Are weight loss supplements safe?
Prescription weight loss medications undergo rigorous safety testing. Side effects are common (nausea, diarrhoea) but usually manageable. OTC supplements have varying evidence—check with your GP before starting any, especially if you take other medications or have health conditions.
How much weight will I lose with weight loss supplements?
Results vary significantly between individuals. Wegovy users in clinical trials lost an average of 15% body weight; Mounjaro users averaged 15–21%. Results depend on dose, adherence, diet, exercise, and personal metabolism. Your GP or prescriber can discuss realistic expectations.
What eligibility criteria apply for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, high blood pressure, heart disease) may be eligible. South Asian, Chinese, Black African, and Caribbean adults may qualify at lower BMI thresholds. A prescriber assesses individual suitability.
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.