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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GLP-1 Medication for Weight Loss in the UK
GLP-1 medications are prescription-only weight loss injections now available in the UK to help eligible adults manage their weight. These prescription weight loss options, including Mounjaro (tirzepatide) and Wegovy (semaglutide), work by mimicking natural hormones that regulate appetite and fullness. If you have a BMI of 30 or above, or 27 with weight-related health conditions like type 2 diabetes or high blood pressure, you may be eligible for prescription weight loss medication through NHS specialist services or private prescribing. Our free GLP-1 weight loss calculator can help you explore potential outcomes, while our BMI calculator shows whether you fall within the eligibility range.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 GLP-1 Medications for Weight Management
Three GLP-1 and GIP/GLP-1 medications are currently licensed in the UK for weight loss in eligible adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, injected once weekly. Maximum dose is 15mg. Clinical trials showed an average weight loss of approximately 15–21% of body weight alongside diet and exercise.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, injected once weekly up to 2.4mg. Average weight loss in trials was around 15% of body weight.
- Saxenda (liraglutide) — a GLP-1 receptor agonist, injected once daily up to 3mg. Results typically range from 5–clinically studied weight loss.
All three are prescription-only medicines available in the UK and require a clinical assessment to confirm eligibility. Individual results vary significantly based on lifestyle, genetics, and adherence to reduced-calorie diet and physical activity recommendations.
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 Access vs Private Weight Loss Medication
NHS Access: GLP-1 medications are approved by NICE for use within specialist weight management services (Tier 3/4). You'll need a referral from your GP, though NHS availability varies significantly by region and waiting times can be lengthy.
Private Access: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. This route doesn't require NHS referral and medications can be dispensed more quickly, though there is a cost involved.
Whether through NHS or private routes, eligibility is based on BMI and health factors. Your GP is the best starting point — they can assess your individual situation, discuss whether prescription weight loss medication is appropriate for you, and outline your options within your local NHS services.
- 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 GLP-1 medication and how does it work for weight loss?
GLP-1 medications mimic a natural gut hormone that regulates appetite and blood sugar. They signal fullness to your brain, reduce food cravings, and slow stomach emptying, helping you feel satisfied with smaller meals. They work best alongside a reduced-calorie diet and increased physical activity.
Am I eligible for GLP-1 weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free BMI calculator to check where you fall, then discuss eligibility with your GP.
How much weight can I expect to lose with GLP-1 medication?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary considerably. Some people lose more, some less. Results depend on adherence to lifestyle changes, genetics, and the specific medication and dose. Your prescriber can discuss realistic expectations.
What's the difference between NHS and private GLP-1 medication in the UK?
NHS access requires GP referral to specialist weight management services and varies by region; private access is available through online prescribing without NHS referral but involves costs. Both routes require clinical assessment and prescription from a UK-licensed prescriber.
What are the common side effects of GLP-1 weight loss medication?
Most commonly, nausea, diarrhoea, constipation, and stomach discomfort—typically during dose escalation. These often improve over time. Serious side effects are rare but include severe stomach pain and allergic reactions. Always discuss side effects with your prescriber and report any concerns.
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.