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
How Does Metformin Work For Weight Loss?
Metformin is a prescription medication primarily used to manage type 2 diabetes, but some people experience modest weight loss when taking it. Unlike dedicated weight loss injections, metformin doesn't work through appetite suppression — instead, it affects how your body handles glucose and insulin. This guide explains the mechanism behind metformin's weight loss effects and how it compares to other prescription weight loss options available in the UK.
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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.
How Metformin Affects Weight
Metformin works through several mechanisms that may contribute to weight loss. It reduces the amount of glucose your liver produces, which lowers blood sugar levels and reduces insulin spikes after meals. Elevated insulin can promote fat storage, so lower insulin levels may reduce this effect. Metformin also improves insulin sensitivity — meaning your cells use glucose more efficiently — which can reduce overall appetite and cravings.
Additionally, metformin may alter gut bacteria composition and reduce absorption of some carbohydrates in the small intestine. These changes can lead to feeling fuller for longer and consuming fewer calories without deliberately restricting diet. However, weight loss with metformin is typically modest — averaging 2–3 kg (4–7 lbs) over several months — and is far less significant than what dedicated GLP-1 weight loss injections achieve.
Metformin is not licensed for weight loss in the UK. Any weight loss is considered a secondary benefit when the medication is used to manage type 2 diabetes or prediabetes.
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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.
Metformin vs GLP-1 Weight Loss Injections
If you're exploring prescription weight loss options in the UK, it's important to understand the difference. GLP-1 receptor agonist medications like Wegovy (semaglutide) and Mounjaro (tirzepatide) are specifically licensed for weight management and deliver far more significant results — averaging 15–clinically studied weight loss in clinical trials.
GLP-1 medications actively reduce appetite and increase feelings of fullness, whereas metformin's weight loss effect is incidental. Your GP can assess whether metformin (if you have prediabetes or type 2 diabetes), a dedicated GLP-1 weight loss injection, or another approach is most appropriate for your individual health goals. Use our free GLP-1 weight loss calculator to explore potential outcomes with licensed weight loss medications, and our BMI calculator to understand your current health status.
- 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.
Can I take metformin just for weight loss without diabetes?
No. Metformin is not licensed for weight loss in the UK and is not routinely prescribed for weight loss alone. It's prescribed for type 2 diabetes, prediabetes, or polycystic ovary syndrome (PCOS). Your GP can discuss whether you meet criteria for metformin based on your blood sugar levels and health history.
How much weight can I expect to lose on metformin?
Weight loss with metformin is typically modest — averaging 2–3 kg over several months when used for diabetes management. This is far less than with GLP-1 weight loss injections, which average 15–clinically studied weight loss. Individual results vary significantly.
Is metformin safer than weight loss injections?
Both metformin and GLP-1 injections have established safety profiles when prescribed appropriately. Metformin has been used for decades and is very well-tolerated. GLP-1 injections are newer but have strong clinical trial data. The choice depends on your individual health, whether you have diabetes, and your goals — your GP can advise.
How long does it take to see weight loss on metformin?
Any weight loss typically appears gradually over 2–3 months of consistent use. Metformin's primary benefit is blood sugar control; weight loss is a secondary effect. If significant weight loss is your main goal, your GP may discuss other options like GLP-1 medications.
Can I combine metformin with weight loss injections?
This depends on your individual health circumstances. Some people with type 2 diabetes take both metformin (for glucose control) and GLP-1 medications (for weight loss). However, any combination must be prescribed and monitored by your GP or specialist — never combine medications without medical guidance.
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.