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
Can I Take Mounjaro With Metformin?
Yes, Mounjaro (tirzepatide) can be taken alongside metformin, and many people in the UK use both medications together. However, there are important interaction considerations you need to know. Metformin is a diabetes medication that helps control blood sugar, while Mounjaro is a dual GIP and GLP-1 receptor agonist licensed for weight management in adults. If you're taking metformin and considering Mounjaro, or already using both, it's essential to understand how they work together and ensure your prescriber has a complete picture of your current medications.
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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.
How Mounjaro and Metformin Interact
Mounjaro and metformin have no direct chemical interaction — they work through different mechanisms and can safely be used together. However, their combined effect on blood sugar and appetite requires careful monitoring:
- Metformin reduces glucose production in the liver and improves insulin sensitivity
- Mounjaro stimulates insulin release in response to food and reduces appetite
- Together, they may lower blood sugar more effectively than either alone
- This combined effect means your blood sugar levels should be monitored regularly
- Your prescriber may need to adjust your metformin dose if you start Mounjaro
- If you take insulin or other diabetes medications alongside metformin, additional adjustments may be needed
Always inform your prescriber that you take metformin before starting Mounjaro, even if it's a private prescription.
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.
What Your Prescriber Needs to Know
When seeking a Mounjaro prescription — whether through NHS specialist weight management services or a private online prescriber — you must disclose that you're taking metformin. Your prescriber will review your current blood sugar control, recent HbA1c results, and kidney function before approving Mounjaro, as both medications are processed through the kidneys.
Do not start or stop metformin without discussing it with your GP or the prescriber issuing your Mounjaro KwikPen. If you experience unusual symptoms like extreme fatigue, dizziness, or rapid heart rate after starting Mounjaro, contact your GP immediately — these could indicate blood sugar changes.
- 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.
Will Mounjaro replace my metformin?
No. Mounjaro is a weight management injection, not a replacement for diabetes treatment. Metformin remains your diabetes medication. Your prescriber may adjust the metformin dose based on how your blood sugar responds to Mounjaro, but the two medications serve different purposes and are often used together.
Can I start Mounjaro if I've just started metformin?
Yes, but inform your prescriber. If metformin is very new, your blood sugar may still be stabilising. Your prescriber will assess whether it's the right time to add Mounjaro or whether to wait. They'll consider your full medical history and current blood sugar control.
Does metformin affect how Mounjaro works?
Metformin doesn't reduce Mounjaro's effectiveness. However, the combined glucose-lowering effect may be stronger than Mounjaro alone, which is why monitoring is important. This combined effect can actually be beneficial for people with type 2 diabetes, but it requires oversight.
What if I'm on metformin and other diabetes medicines?
Tell your prescriber about all diabetes medications — metformin, insulin, sulphonylureas, or others. Mounjaro may increase the effect of these drugs, so your prescriber may reduce doses to prevent low blood sugar (hypoglycaemia). Never adjust doses yourself.
Can I use our GLP-1 weight loss calculator if I take metformin?
Yes. Our free weight loss calculator estimates potential outcomes with Mounjaro, but it doesn't replace professional medical assessment. If you take metformin, your prescriber will give you personalised guidance on realistic expectations alongside your current diabetes management.
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.