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 Peptides for Weight Loss in the UK
Peptides used for weight loss in the UK are actually prescription medications called GLP-1 and GIP receptor agonists. The most effective options available are Mounjaro (tirzepatide) and Wegovy (semaglutide), both licensed by the MHRA for weight management. These medications work by helping regulate appetite and food intake. Access varies between NHS specialist services and private prescribing. Our GLP-1 weight loss calculator can help you understand potential outcomes, whilst your GP can assess whether you're eligible.
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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 Peptide Medications
The best peptides for weight loss medication in the UK are prescription-only injectables:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, once-weekly injection, doses from 2.5mg to 15mg. Clinical trials showed average weight loss of 15–21% body weight alongside lifestyle changes.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, once-weekly injection, doses from 0.25mg to 2.4mg. STEP trial data showed average weight loss around 15% body weight.
- Saxenda (liraglutide) — a GLP-1 receptor agonist, daily injection, maximum 3mg. Available but less commonly prescribed than Mounjaro and Wegovy.
All three are available in the UK through prescription only, following a clinical assessment. Individual results vary significantly. These medications are typically used alongside reduced-calorie diet and increased physical activity.
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.
NHS vs Private Access — How to Get Started
NHS access: Referral to a tier 3 or tier 4 specialist weight management service through your GP. Availability varies significantly by region. Waiting lists can be lengthy in many areas.
Private access: Online consultation with a UK-licensed prescriber, prescription issued if clinically suitable, dispensed by a GPhC-registered pharmacy. Available without NHS referral.
Eligibility: Adults with BMI 30 or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease). Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. Your GP can confirm whether you qualify and discuss the best option for you.
- 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 peptides for weight loss safe?
GLP-1 and GIP receptor agonist medications are prescription-only and have been through MHRA approval. Like all medicines, they have potential side effects, most commonly nausea, diarrhoea, and constipation. These typically improve over time. Serious side effects are rare but can include pancreatitis. Your prescriber will assess suitability based on your individual health and monitor you during treatment.
How much weight can I expect to lose with peptides?
Clinical trials showed average weight loss of 15–21% body weight over 68–72 weeks with Mounjaro, and around 15% with Wegovy. Individual results vary significantly based on genetics, lifestyle, dose, and adherence. Weight loss requires sustained effort with diet and physical activity — medications support this process but aren't a standalone solution. Use our GLP-1 weight loss calculator to explore potential outcomes.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1-only agonist. Mounjaro may produce slightly greater weight loss on average, though results vary. Both are once-weekly injections. Both require prescription and clinical assessment. Your prescriber will recommend the most suitable option based on your health profile and individual circumstances.
Can I get weight loss peptides on the NHS?
Yes, if you meet eligibility criteria and are referred to a specialist tier 3 or tier 4 weight management service. However, NHS availability varies by region (ICB), and waiting lists can be very long. Private prescribing is available without NHS referral if you prefer faster access. Either way, a clinical assessment is required before any prescription is issued.
Are peptide weight loss injections the same as cosmetic injections?
No. Prescription weight loss medications like Mounjaro and Wegovy are therapeutic medicines approved by the MHRA for managing excess weight and related health conditions. They are completely different from cosmetic injectables. They work by regulating hormones and appetite. You need a prescription and clinical assessment to access them legally in the UK.
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.