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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Gut Weight Loss — UK Prescription Medication Options
If you're looking to lose weight and have heard about "gut weight loss" medications, you're likely referring to GLP-1 receptor agonist injections — prescription medicines that work by affecting appetite signals in your digestive system. Several options are now available in the UK for eligible adults. This guide explains which medications are licensed for weight management, how they work, who can access them on the NHS or privately, and how to start a conversation with your GP about whether prescription weight loss medication might be right for you.
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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 Explained
Three prescription medications are currently licensed in the UK specifically for weight management, all of which work on the gut-brain appetite pathway:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist given as a once-weekly injection. In clinical trials, participants lost an average of 15–21% of their body weight alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — A GLP-1 receptor agonist given as a once-weekly injection. Clinical trials showed an average weight loss of around 15% of body weight at the highest dose.
- Saxenda (liraglutide) — A GLP-1 receptor agonist given as a once-daily injection, with slightly different dosing and lower average weight loss than the weekly options.
All three are prescription-only medicines and require clinical assessment before being prescribed. Individual results vary significantly — some people lose more weight, some less. These medications work best when combined with lifestyle changes including a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential weight loss outcomes at different doses.
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 Access vs Private Prescription Weight Loss
NHS route: Prescription weight loss medication is available through specialist tier 3 weight management services in England. You'll need a referral from your GP, and you must meet NHS weight management criteria (typically BMI of 30 or above, or 27–29.9 with weight-related health conditions). Availability varies significantly by region, and waiting lists can be several months or longer in many areas.
Private route: All three medications are available through UK GPhC-registered online pharmacies following a consultation with a licensed prescriber. You don't need an NHS referral, and treatment can usually start within days. Costs vary depending on the medication and dose, typically ranging from £129–£320 per month.
To find out if you're eligible, book an appointment with your GP or use our free BMI calculator above to check your starting point. Your GP can discuss which option — NHS or private — is most appropriate for your circumstances.
- 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.
How do gut weight loss medications actually work?
These medications activate GLP-1 (and in Mounjaro's case, GIP) receptors in your gut and brain. This signals fullness, reduces appetite and food cravings, and slows how quickly food leaves your stomach. The effect helps you eat less naturally without feeling deprived, making it easier to stick to a reduced-calorie diet alongside lifestyle changes.
Am I eligible for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with at least one weight-related health condition (type 2 diabetes, high blood pressure, heart disease, sleep apnoea, etc.). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. Your GP or a licensed prescriber can assess your individual eligibility.
How much weight can I expect to lose with these medications?
Clinical trials show average weight loss of 15–21% of body weight over 68–72 weeks, but individual results vary significantly. Some people lose more, some less. Weight loss also depends on your diet, activity level, and adherence to treatment. It's important to have realistic expectations — these medications support weight loss but aren't a assures.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is a single GLP-1 agonist. In trials, Mounjaro showed slightly higher average weight loss (up to 21% vs 15%). Mounjaro doses up to 15mg weekly; Wegovy up to 2.4mg weekly. Both are once-weekly injections. Your prescriber will recommend which suits you best.
Can I get these medications through the NHS or do I have to go private?
Both options exist in the UK. NHS access is through tier 3 specialist weight management services (referral needed, variable waiting lists). Private access is through online prescribing services (faster, no referral needed, costs apply). Talk to your GP about which route is appropriate for you — they can discuss NHS availability in your area.
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.