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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Metformin and Weight Loss — Doses and Effectiveness
Metformin is a widely prescribed diabetes medication that may support modest weight loss in some people, but it's not licensed specifically for weight management in the UK. If you're exploring weight management options, understanding metformin's role alongside other evidence-based approaches—including lifestyle changes and, where appropriate, prescription GLP-1 medications like Wegovy or Mounjaro—can help you make informed decisions with your GP. This guide covers metformin dosing and its realistic weight loss potential.
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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 May Support Weight Loss
Metformin (often prescribed as Glucophage) is primarily approved for managing type 2 diabetes and prediabetes. While it may support modest weight loss—typically 2–3 kg on average—it works differently from GLP-1 weight loss injections. Metformin improves how your body handles blood sugar and may reduce appetite slightly, but weight loss is not its main purpose.
Standard metformin dosing:
- Starting dose: 500 mg once or twice daily
- Maintenance: 1,500–2,000 mg daily (split into 2–3 doses)
- Maximum: typically 2,550 mg daily
Doses are increased gradually over weeks to reduce stomach side effects. If weight loss is your primary goal, your GP may discuss whether prescription weight loss medications like GLP-1 injections could be more effective for your individual situation.
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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
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Metformin vs. GLP-1 Weight Loss Medications
Unlike Wegovy (semaglutide) or Mounjaro (tirzepatide)—which are licensed specifically for weight management—metformin is a diabetes medication with modest weight loss as a side benefit. Clinical trials show GLP-1 medications help participants lose an average of 15–21% of body weight, compared to 2–3 kg with metformin alone.
If you have a BMI of 30 or above, or 27 or above with weight-related health conditions like prediabetes, your GP may discuss whether prescription weight loss treatment could be more suitable alongside diet and physical activity. Use our free BMI calculator to check your BMI, then discuss all options with your GP.
- 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 standard metformin dose for weight loss?
Metformin is not licensed for weight loss. Standard diabetes doses range from 500 mg to 2,550 mg daily. Weight loss, if it occurs, is modest (typically 2–3 kg). Dosing is individualised and must be prescribed by your GP based on your kidney function and health. Always follow your GP's guidance.
How much weight can I expect to lose with metformin?
Average weight loss with metformin is approximately 2–3 kg. Results vary widely and depend on diet, activity level, and individual metabolism. Metformin works best alongside lifestyle changes. If greater weight loss is your goal, ask your GP about prescription weight loss medications licensed in the UK.
Is metformin licensed for weight management in the UK?
No. Metformin is licensed for type 2 diabetes and prediabetes management. Weight loss is an occasional side effect, not the primary purpose. Wegovy and Mounjaro are the UK-licensed medications specifically approved for weight management in eligible adults.
Can I take metformin with Wegovy or Mounjaro?
This depends on your individual situation and current medications. If you're already taking metformin for diabetes or prediabetes and are considering GLP-1 medication, discuss it with your GP or prescriber. They can assess whether it's safe to use both together and adjust doses if needed.
What are common side effects of metformin?
Common side effects include stomach upset, nausea, diarrhoea, and metallic taste. These often improve with gradual dose increases. Serious side effects are rare but include lactic acidosis (very rare). Report persistent side effects to your GP—they may adjust your dose or suggest alternatives.
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.