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 Peptide For Weight Loss In The UK
If you're looking for the best peptide for weight loss in the UK, prescription options are available for eligible adults. Three GLP-1 and dual GIP/GLP-1 receptor agonist medications are currently licensed for weight management: Mounjaro, Wegovy, and Saxenda. These peptide injections work by signalling to your brain that you're full, reducing appetite and food cravings. Access depends on eligibility, which your GP can assess. Use our free BMI calculator to check where you stand, then speak with your healthcare provider about prescription weight loss options.
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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 Peptides And How They Work
Three prescription peptides are licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, once-weekly injection, doses from 2.5 mg to 15 mg. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks alongside reduced-calorie diet and increased physical activity. Individual results vary significantly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, once-weekly injection, doses up to 2.4 mg. STEP trial data showed average weight loss of approximately 15% body weight. Results vary between individuals.
- Saxenda (liraglutide) — a GLP-1 receptor agonist, daily injection, doses up to 3 mg. All three require a prescription following clinical assessment. None clinically studied weight loss — they're used alongside lifestyle changes, not instead of them.
Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses, though actual results depend on your individual circumstances and adherence to diet and exercise changes.
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 Weight Loss Peptides In The UK
In the UK, you may be eligible for prescription weight loss peptides if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease). Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS route: Ask your GP for a referral to a tier 3 specialist weight management service. Availability and waiting times vary significantly by region. Private route: Online consultations with UK-licensed prescribers are available without NHS referral, though these are not free. Start by speaking with your GP about what's right for you — they can assess your individual health and discuss all options.
- 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 difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs ~15%), but individual results vary. Both are once-weekly injections. Your prescriber will assess which is suitable for your health profile.
Can I get weight loss peptides on the NHS in the UK?
Yes, but access is through specialist tier 3 weight management services, not standard GP prescription. You'll need a GP referral and must meet eligibility criteria (BMI ≥30, or ≥27.5 with comorbidities). Waiting lists vary by region — some areas have significant delays. Private options are available without NHS referral.
How much weight will I lose on a weight loss peptide?
Clinical trials show average weight loss of 15–21% of body weight over several months, but individual results vary significantly. Some people lose more, some less. Weight loss peptides work best when combined with reduced-calorie diet and increased physical activity. Results depend on adherence, starting weight, metabolism, and other factors.
Are weight loss peptides safe, and what side effects should I expect?
All three UK-licensed peptides are prescription-only and undergo rigorous safety testing. Common side effects include nausea, constipation, diarrhoea, and stomach discomfort — usually mild and temporary. Serious side effects are rare but can include pancreatitis (severe stomach pain). Your GP will assess whether peptides are safe for your individual health before prescribing.
What happens when you stop taking weight loss peptides?
When you stop, appetite and hunger signals typically return to normal over weeks to months. Some people regain weight, others maintain it — this depends on whether lifestyle changes (diet and exercise) become permanent habits. Peptides are designed as part of a long-term weight management approach, not a structured approach. Your GP can discuss ongoing support strategies.
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.