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 You Take Insulin and Mounjaro at the Same Time?
Yes, you can take insulin and Mounjaro together, but it requires careful medical management. Mounjaro (tirzepatide) is not insulin — it's a dual GIP and GLP-1 receptor agonist that works differently. However, because both medications affect blood sugar control, your GP or prescriber will need to monitor you closely and may adjust your insulin doses to prevent low blood sugar (hypoglycaemia). Always inform your prescriber if you're already taking insulin before starting Mounjaro, and never adjust insulin doses yourself.
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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 Insulin and Mounjaro Interact
Mounjaro and insulin work through different mechanisms, but both lower blood sugar, which means combining them increases the risk of hypoglycaemia (dangerously low blood sugar levels). Mounjaro is a GLP-1 and GIP receptor agonist that stimulates insulin release in response to food and slows stomach emptying, while insulin directly replaces or supplements the body's natural insulin production. When used together, your prescriber will typically reduce your insulin dose — particularly if you take a sulphonylurea or insulin — to maintain safe blood sugar levels.
- Your blood sugar will need regular monitoring through fingertip testing or continuous glucose monitoring (CGM)
- Your insulin requirements may decrease significantly, especially as Mounjaro doses increase
- If you experience signs of hypoglycaemia (shakiness, sweating, confusion, rapid heartbeat), treat immediately with fast-acting carbohydrates and contact your healthcare team
- Never stop either medication without guidance from your prescriber
This is why Mounjaro prescribing in the UK always requires a clinical assessment and ongoing medical supervision, particularly if you're already on insulin therapy.
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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.
NHS Prescribing and Your GP's Role
In the UK, if you're taking insulin and considering Mounjaro, your GP or specialist prescriber must be fully aware of your insulin regimen before issuing a Mounjaro prescription. NHS tier 3 specialist weight management services are experienced in managing patients on multiple glucose-lowering therapies. Whether you access Mounjaro through the NHS or privately, the prescriber will assess your current insulin dose, your HbA1c (long-term blood sugar control), and your kidney function before starting.
- Your GP should monitor you more frequently when starting Mounjaro — typically blood tests and reviews every 2–4 weeks during dose titration
- Inform your prescriber immediately if you experience persistent sickness, severe abdominal pain, or signs of pancreatic problems
- Keep your GP updated with any changes to your insulin doses or blood sugar patterns
- 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 reduce how much insulin I need?
Yes, very likely. Because Mounjaro helps regulate blood sugar by stimulating insulin release and slowing food absorption, many patients require lower insulin doses. Your prescriber will adjust this carefully based on your blood sugar readings. Never reduce insulin yourself — always consult your GP or prescriber first.
What are the signs of low blood sugar when taking both medications?
Hypoglycaemia symptoms include shakiness, sweating, dizziness, confusion, rapid heartbeat, and feeling very hungry. If you experience these, treat immediately with 15 grams of fast-acting carbohydrates (glucose tablets, fruit juice, or sugar), then recheck your blood sugar after 15 minutes. Contact your healthcare team if symptoms persist.
Can I start Mounjaro if I'm currently on insulin?
Yes, but you'll need a clinical assessment from a prescriber who is aware of your insulin therapy. Do not start Mounjaro without informing your healthcare provider about all your current medications, including insulin. Your prescriber will plan a safe approach to combining them.
How often will my blood sugar be monitored?
During the initial titration phase (first 16–20 weeks), expect more frequent monitoring — typically every 2–4 weeks with blood tests and clinical review. Once you've reached your target Mounjaro dose and insulin levels are stable, monitoring may become less frequent, but ongoing supervision is essential.
What if I experience severe stomach pain while on both medications?
Severe stomach pain, especially if it spreads to your back, could indicate pancreatitis or gallbladder problems. This is a medical emergency. Seek urgent medical attention at A&E or call 111. Inform them you're taking Mounjaro and insulin. Do not wait for a routine GP appointment if you have severe, persistent abdominal pain.
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.