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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How Does Mounjaro Work For Diabetes
Mounjaro (tirzepatide) is a prescription-only injectable medicine that works differently in the body depending on whether it's prescribed for type 2 diabetes or weight management. Originally developed and approved for type 2 diabetes treatment, it's now also licensed for weight management in the UK. Understanding how Mounjaro works can help you discuss its benefits and suitability with your GP. This guide explains the mechanisms behind this dual-action medication and how it supports blood sugar control in people with diabetes.
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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's Dual Mechanism Works in Diabetes
Mounjaro is a dual GIP and GLP-1 receptor agonist — this dual action is what makes it unique. It activates two separate hormone pathways in the body that regulate blood sugar. The GLP-1 pathway stimulates the pancreas to release insulin in response to food, particularly when blood sugar is elevated. The GIP pathway (glucose-dependent insulinotropic polypeptide) also enhances insulin secretion but only when blood sugar is high, helping prevent low blood sugar episodes. Together, these mechanisms help bring elevated glucose levels back to normal range. Mounjaro also reduces glucagon release — a hormone that would otherwise raise blood sugar — and slows gastric emptying, meaning food moves through the stomach more gradually, which helps prevent sharp spikes in blood sugar after meals. This multi-layered approach is why Mounjaro may be more effective for some people than single-hormone medications like semaglutide (found in Wegovy), which only activates the GLP-1 pathway.
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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.
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Mounjaro Dose Titration and Diabetes Management
In type 2 diabetes management, Mounjaro is started at a low dose and gradually increased over several weeks — a process called dose titration. This allows your body to adapt and helps minimise side effects. Your GP or specialist will monitor your HbA1c level (a measure of average blood sugar over 3 months) and adjust your dose based on how well your blood sugar is controlled. Doses are increased approximately every 4 weeks, ranging from 2.5 mg up to 15 mg once weekly. Blood sugar control typically improves over weeks rather than days, so patience is important. You'll also need regular check-ups to monitor kidney function and other health markers. If you're already taking other diabetes medications like metformin or insulin, your GP may need to adjust those doses when starting Mounjaro to avoid blood sugar dropping too low.
- 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.
Is Mounjaro the same as Ozempic?
Both contain semaglutide, but they're not the same. Ozempic contains semaglutide and is licensed for type 2 diabetes only (not weight loss). Mounjaro contains tirzepatide and is licensed for both diabetes and weight management in the UK. Mounjaro's dual GIP/GLP-1 action differs from semaglutide's single GLP-1 action, potentially offering better blood sugar control for some people.
How long does it take Mounjaro to work for diabetes?
Blood sugar improvements typically begin within the first few weeks, but full benefits may take 8–12 weeks as your body adjusts and your dose increases. HbA1c levels (average blood sugar over 3 months) usually improve after 3 months of consistent use. Your GP will monitor progress through blood tests.
Will Mounjaro replace my other diabetes medications?
Possibly, but only your GP or diabetes specialist can decide. Some people reduce or stop other medications once Mounjaro is working well. Others continue taking complementary medicines like metformin. Never stop or adjust any diabetes medication without medical guidance, as blood sugar management requires careful coordination.
Can Mounjaro cause low blood sugar (hypoglycaemia)?
Mounjaro alone rarely causes dangerously low blood sugar. However, if you're also taking insulin or medications like sulphonylureas, the combined effect may lower blood sugar too much. Your prescriber will adjust these medications and teach you to recognise low blood sugar symptoms.
Is Mounjaro available on the NHS for type 2 diabetes?
Yes, Mounjaro is available on the NHS for type 2 diabetes management through specialist tier 3 services or your GP practice, depending on local arrangements. Access and waiting times vary significantly by region. Your GP can discuss eligibility and refer you if appropriate.
Ready to take control of your weight loss journey?
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