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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Hypoglycaemia Risk: Mounjaro vs Wegovy Compared
Hypoglycaemia (low blood sugar) is a potential side effect when taking weight loss injections like Mounjaro and Wegovy, particularly if you also take diabetes medications. Both medications work differently — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only — which may affect hypoglycaemia risk differently. Understanding how each medication works and what the clinical evidence shows can help you and your GP make an informed decision about which is right for you. This guide compares both medications based on trial data and UK clinical guidance.
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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 and Wegovy Affect Blood Sugar
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. The dual mechanism activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This means Mounjaro stimulates insulin release in response to food more directly than GLP-1-only medications. In clinical trials, Mounjaro demonstrated effective blood sugar control in people with type 2 diabetes, but this also carries a higher theoretical risk of hypoglycaemia when combined with other diabetes medications that lower blood sugar.
Wegovy (semaglutide) is a GLP-1 receptor agonist only. It works through a single hormone pathway, which means it has a gentler effect on insulin release compared to Mounjaro's dual action. Wegovy's STEP trials showed modest effects on blood sugar but lower rates of hypoglycaemia when used for weight loss in people without diabetes. However, if you take diabetes medications alongside Wegovy, hypoglycaemia remains possible.
Both medications slow gastric emptying (how quickly food leaves your stomach), which also helps regulate blood sugar levels. The key difference is mechanism: dual action (Mounjaro) vs single action (Wegovy).
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Which Medication Carries Lower Hypoglycaemia Risk?
In weight loss trials, hypoglycaemia was more commonly reported in people taking Mounjaro than Wegovy, particularly in those also taking diabetes medications like insulin or sulphonylureas. However, individual risk depends heavily on your personal circumstances: current medications, diabetes status, kidney function, and how your body responds to the injection.
If you take diabetes medications, your prescriber may need to adjust doses when you start either medication. Some people require lower doses of insulin or may need to stop sulphonylureas altogether. This decision is always made by your prescriber following a clinical assessment — never adjust diabetes medication yourself.
If you have a history of hypoglycaemia or take multiple diabetes medications, discuss this explicitly with your GP before starting either injection. They can assess which medication carries lower risk for you personally.
- 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 Mounjaro cause hypoglycaemia in people without diabetes?
Hypoglycaemia is rare in people without diabetes taking Mounjaro for weight loss alone, as the medication only stimulates insulin when blood sugar rises after eating. However, if you take other diabetes medications, the risk increases significantly. Always inform your prescriber of all medications.
Is Wegovy safer than Mounjaro if I take insulin?
Wegovy may carry lower hypoglycaemia risk than Mounjaro in people taking insulin, due to its single GLP-1 mechanism versus Mounjaro's dual GIP+GLP-1 action. However, both require careful monitoring. Your prescriber will assess which is safer for your individual situation.
What symptoms of hypoglycaemia should I watch for?
Symptoms include shakiness, sweating, rapid heartbeat, anxiety, dizziness, blurred vision, and difficulty concentrating. If you experience these, eat or drink fast-acting carbohydrates (glucose tablets, fruit juice, regular soft drink) and contact your GP. Carry emergency glucose identification.
Will my diabetes medication doses need to change if I start Mounjaro or Wegovy?
Yes — many people require lower doses of diabetes medications when starting either injection. Your prescriber will monitor blood sugar levels and adjust doses as needed. Never adjust diabetes medications yourself; always follow your prescriber's guidance.
How do SURMOUNT and STEP trials relate to hypoglycaemia risk?
SURMOUNT (Mounjaro) and STEP (Wegovy) are clinical trials studying weight loss outcomes. Both trials tracked hypoglycaemia as a side effect, with Mounjaro showing higher rates in people taking other diabetes medications. However, these trials focused on weight loss, not diabetes management — your GP can explain specific trial findings relevant to your health.
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