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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What's the Difference Between Wegovy and Mounjaro?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight management injections licensed in the UK, but they work differently and have different dosing schedules. This guide explains the key differences so you can understand what your prescriber might discuss with you. Both are once-weekly injections, but Mounjaro uses a dual mechanism while Wegovy uses a single GLP-1 pathway. Individual suitability depends on your health profile, medical history, and how your body responds to treatment. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to understand your current health context.
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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 Wegovy and Mounjaro Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in the body. This dual mechanism may support appetite regulation, cravings reduction, and feeling fuller after smaller meals. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway.
Clinical trial results: In the SURMOUNT-1 trial, Mounjaro achieved average weight loss of approximately 15–21% of body weight at maximum dose. In the STEP-1 trial, Wegovy achieved average weight loss of approximately 14.9% of body weight. These are clinical averages — individual results vary significantly and are influenced by diet, activity, and personal metabolism.
Both slow gastric emptying (how quickly food leaves the stomach), though this effect typically reduces over time. Both are prescription-only and require a clinical assessment before being prescribed.
Clinically BackedWeight Loss
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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.
Dosing, Side Effects, and Prescriber Choice
Dosing: Wegovy starts at 0.25 mg and titrates to a maximum of 2.4 mg over 16 weeks. Mounjaro starts at 2.5 mg and titrates to a maximum of 15 mg over approximately 20 weeks. Both are once-weekly injections. Your prescriber will determine which dose and escalation schedule suits you.
Side effects are similar for both: nausea, diarrhoea, constipation, and stomach pain are most common. Serious side effects are rare but can include pancreatitis symptoms or gallbladder issues.
Whether your prescriber recommends Wegovy or Mounjaro depends on your individual health profile, any medications you take, previous treatment responses, and their clinical experience. Both are valid options. Ask your prescriber to explain their recommendation for you.
- 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 more effective than Wegovy for weight loss?
Clinical trials show both achieve similar average weight loss (around 15–21% body weight). Mounjaro's dual mechanism may appeal to some, but individual responses vary. Neither is assured to work better for you personally. Your prescriber will assess which is most appropriate based on your health profile.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching between them is possible, but must be managed by your prescriber. There is no official conversion chart — your prescriber will determine safe switching based on your current dose and response. Never switch medications without medical guidance.
Do Wegovy and Mounjaro cost the same in the UK?
Private costs vary by dose and provider, typically ranging from £129–£320 per month for either medication. NHS access is limited to specialist tier 3 services where availability varies by region. Ask your prescriber or pharmacy for current pricing.
Which injection sites do Wegovy and Mounjaro use?
Both can be injected into the stomach, upper thigh, or upper arm. Rotate injection sites weekly to reduce irritation. Both come as pre-filled pens. Follow your prescriber's guidance on injection technique.
How long does it take to see weight loss results with either medication?
Most people see initial weight loss within 2–4 weeks, though results vary. Maximum weight loss is typically seen at 12–16 weeks on a stable dose. Consistent diet and activity changes alongside the injection support better outcomes. ```
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.