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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Safe Weight Loss Supplements and Medications in the UK
When searching for safe weight loss supplements, it's important to know that the most effective evidence-based options available in the UK are prescription medications, not over-the-counter supplements. If you're interested in weight management, prescription weight loss injections like Mounjaro and Wegovy have strong clinical evidence behind them. These are available through both NHS specialist services and private prescribing in the UK. This guide explains what's available, who's eligible, and how to access these options through your GP or a licensed prescriber.
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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
The safest and most clinically proven weight management options in the UK are prescription medications. Three main medications are licensed for weight management in UK adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, dosed from 2.5 mg to 15 mg once weekly. Clinical trials showed average weight loss of 15–21% of body weight when used alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, dosed from 0.25 mg to 2.4 mg once weekly. Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a daily GLP-1 injection, dosed from 0.6 mg to 3 mg. These medications work by helping regulate appetite and promoting feeling fuller after meals.
All three are prescription-only and require clinical assessment before being prescribed. 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.
NHS vs Private Access and How to Get Started
In the UK, weight loss medication is available through two routes: NHS specialist tier 3 services (following referral from your GP) or private prescribing via licensed online pharmacies. NHS access is free but availability varies by region and waiting lists can be lengthy. Private options are available without NHS referral, though there is a cost (typically £130–£320 per month depending on dose). Eligibility criteria are similar: adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your first step is always to speak with your GP about whether weight loss medication might be appropriate for you, or you can access a private clinical assessment through a GPhC-registered online pharmacy. Use our free BMI calculator above to check your current BMI and see where you stand against NHS weight guidelines.
- 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 over-the-counter weight loss supplements safe and effective?
Most over-the-counter supplements lack strong clinical evidence. The most effective and safest weight loss options in the UK are prescription medications like Mounjaro and Wegovy, which have undergone rigorous clinical trials. Always speak to your GP before starting any supplement or medication.
How much weight can I expect to lose with prescription weight loss medication?
In clinical trials, Mounjaro helped participants lose an average of 15–21% of their body weight, and Wegovy approximately 15%. However, individual results vary significantly. Weight loss depends on your starting weight, dose, adherence, diet, and physical activity. Our GLP-1 weight loss calculator can help you see projected results.
Who is eligible for NHS weight loss medication in the UK?
Adults with a BMI of 30 or above are eligible, or those with a BMI of 27–29.9 with at least one weight-related condition such as type 2 diabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply. Your GP can assess your individual eligibility.
How do I access weight loss medication through the NHS?
Ask your GP for a referral to your local tier 3 specialist weight management service. These services assess patients and may prescribe weight loss medication alongside lifestyle support. Waiting times and availability vary significantly by region, so speak to your GP about what's available in your area.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections. Mounjaro is a dual GIP and GLP-1 agonist with average weight loss of 15–21%, while Wegovy is a GLP-1 agonist alone with average weight loss around 15%. They work similarly but Mounjaro activates two hormone pathways. A prescriber will advise which is appropriate for you based on your health profile.
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.