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
Free tracker included with every download this week
Gut Bacteria and Weight Loss — UK Prescription Options
Your gut bacteria plays a significant role in weight management, digestion, and metabolism. While changing your diet and lifestyle can support healthy gut bacteria, prescription weight management medications available in the UK work through different mechanisms to support weight loss. For eligible adults, prescription options like GLP-1 injections offer clinically proven support alongside lifestyle changes. Our free BMI calculator can help you check your starting point, and understanding your eligibility for medication is an important conversation to have with your GP.
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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 Medications — What's Available
Three prescription-only weight management medications are currently licensed in the UK for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist taken once weekly, with clinical trials showing average weight loss of 15–21% of body weight over 72 weeks. Wegovy (semaglutide) is a once-weekly GLP-1 agonist that helped participants lose an average of approximately 15% of body weight in trials. Saxenda (liraglutide) is a daily GLP-1 injection, though it is less commonly prescribed than the weekly options.
All three work by reducing appetite and supporting feelings of fullness, though they work through slightly different mechanisms. Individual results vary, and these medications are most effective when combined with a reduced-calorie diet and increased physical activity. Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses.
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 vs Private Access — How to Get Weight Loss Medication in the UK
NHS access: Weight loss medications are available through specialist tier 3 weight management services, but access varies significantly by region. Your GP can refer you, though waiting lists are often long. Eligibility is assessed by specialist services based on your BMI, health conditions, and previous weight management attempts.
Private access: Available through private online prescribing following a clinical assessment with a UK-licensed prescriber. No NHS referral is needed, though costs range from approximately £129–£320 per month depending on dose. Whichever route you choose, speak with your GP first about whether prescription weight loss medication is appropriate for your health 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 does gut bacteria affect weight loss and metabolism?
Your gut bacteria influences how you digest food, produce short-chain fatty acids, regulate appetite hormones like GLP-1, and control energy storage. A healthy microbiome supports better metabolism, but prescription weight management medications work independently by activating appetite-regulating pathways in your brain.
What is a GLP-1 medication and how does it help with weight loss?
GLP-1 (glucagon-like peptide-1) is a natural hormone your gut produces after eating. GLP-1 medications mimic this hormone, signalling to your brain that you're full, reducing hunger, and slowing how quickly food leaves your stomach. This helps you eat less and feel satisfied on smaller portions.
Am I eligible for prescription weight loss medication on the NHS in the UK?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess your eligibility and refer you to specialist weight management services. For adults of South Asian, Chinese, Black African, or Caribbean heritage, lower BMI thresholds may apply.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight management. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro produced slightly higher average weight loss (15–21% vs ~15%), but both are effective. Your prescriber will recommend the most suitable option for you.
How much weight can I expect to lose with prescription weight loss medication?
Clinical trials showed average weight loss of 15–21% of body weight with Mounjaro and approximately 15% with Wegovy over several months, alongside diet and exercise. However, individual results vary significantly — some people lose more, some less. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss realistic expectations with your prescriber.
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.