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 Fat Loss Medicine in the UK
If you're considering medication to support weight loss, understanding your options is essential. In the UK, several prescription-only medicines are licensed for weight management, each working through different biological pathways to help reduce appetite and support fat loss. These medications are most effective when combined with a reduced-calorie diet and increased physical activity. This guide covers what's available on the NHS, how to access treatment, and what you should expect from prescription weight loss medicine in the UK.
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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-Approved Weight Loss Medicines and How They Work
The UK's medicines regulator (MHRA) has approved three prescription-only weight loss medicines: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are the most commonly prescribed modern options.
- Mounjaro — a dual GIP and GLP-1 receptor agonist that activates two natural hormone pathways to reduce appetite and regulate fat metabolism. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
- Wegovy — a GLP-1 receptor agonist (single mechanism) administered once weekly. In clinical trials, patients achieved approximately 15% average weight loss at the maximum dose of 2.4 mg.
- Saxenda — a daily GLP-1 injection (liraglutide) approved for longer-term weight management, though less frequently prescribed than weekly options.
All three are prescription-only and require a clinical assessment by a licensed healthcare professional before dispensing. None clinically studied weight loss — results depend on adherence, diet, activity levels, and individual metabolism.
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.
Accessing Fat Loss Medicine in the UK: NHS vs Private
NHS access: NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. Access is through tier 3 or 4 services via GP referral, though waiting lists are substantial in many regions. You may wait several months or longer depending on your local Integrated Care Board (ICB) capacity.
Private access: You can obtain prescription weight loss medicine privately through GPhC-registered online prescribers following an online clinical assessment. This route bypasses NHS waiting lists but requires payment. Costs typically range from £129–£320 per month depending on dose and provider. Calculate your personal eligibility and potential results using our free GLP-1 weight loss calculator above. To understand your starting point, try our BMI calculator to assess whether medication eligibility criteria apply to you.
Your GP is your first point of contact for weight loss support. Even if you choose private medication access, discuss this with your GP to ensure it complements any other health conditions or medicines you're taking. Your GP can also refer you to NHS specialist weight management services if you prefer NHS-funded treatment, though this typically involves a waiting period. Prescription weight loss medicines work best alongside behavioural changes — reduced calorie intake, increased physical activity, and sustainable eating patterns produce the most lasting results.
- 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 is the best weight loss medicine available in the UK?
There is no single "best" medicine — suitability depends on your health profile, BMI, medical history, and preferences. Mounjaro and Wegovy are the most modern options approved by MHRA for weight management. Your GP or a licensed prescriber will assess which is appropriate for you following a clinical consultation. Both have strong clinical evidence, though some people respond better to one than the other.
Can I get weight loss medicine on the NHS in the UK?
Yes. NICE has approved tirzepatide (Mounjaro) for NHS use within specialist tier 3 and 4 weight management services. Access requires a GP referral and assessment by specialist clinicians. Availability varies significantly by region, and waiting lists can be lengthy. Private access is faster but requires out-of-pocket costs.
How much weight will I lose on weight loss medicine?
Clinical trials show an average of 15–clinically studied weight loss with modern GLP-1 and GIP/GLP-1 medicines, though individual results vary considerably. Some people lose more, some less. Weight loss is not assured and depends on medication dose, diet adherence, physical activity, and personal metabolism. Results are best when medication is combined with sustained lifestyle changes.
Are weight loss injections safe in the UK?
Prescription weight loss medicines approved by the MHRA (Mounjaro, Wegovy, Saxenda) have undergone rigorous safety testing. However, all medicines carry potential side effects — most commonly nausea, diarrhoea, and vomiting, which often reduce over time. Serious side effects are rare but possible. A healthcare professional will assess whether these medicines are safe and suitable for you specifically before prescribing.
Do I need my GP's permission to use weight loss medicine?
Yes — weight loss medicines are prescription-only, meaning a licensed prescriber (GP or private prescriber) must assess your health, medical history, and current medications before issuing a prescription. Even if you access medication privately, it's advisable to inform your GP so they're aware of your weight loss treatment and can monitor any interactions with other medicines you may be taking.
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.