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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Mounjaro 5 Mg Weight Loss vs Wegovy: What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections licensed in the UK, and both have shown effectiveness in clinical trials. However, they work differently and produce varying results. At the 5 mg Mounjaro dose specifically, understanding how it compares to Wegovy can help you and your prescriber determine which weekly weight loss injection might be more suitable for your individual circumstances. This guide compares the two side-by-side using clinical evidence and UK prescribing context.
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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 5 mg and Wegovy Work Differently
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways in the body — both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may help regulate appetite, reduce cravings, and support feeling fuller after smaller meals.
Wegovy is a GLP-1 receptor agonist only, activating just the GLP-1 pathway. Both medications slow gastric emptying and signal satiety to the brain, but Mounjaro's dual action is the key difference.
In the SURMOUNT-1 clinical trial, Mounjaro 5 mg produced an average weight loss of approximately 15% of body weight over 72 weeks, alongside reduced-calorie diet and exercise. Wegovy (in the STEP trials) showed average weight loss of approximately 14.9% body weight. Individual results vary significantly, and these are clinical trial averages — your results depend on adherence, lifestyle changes, and your body's response.
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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.
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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Practical Differences: Dose, Cost, and NHS Access
Mounjaro 5 mg is typically an escalation dose (usually weeks 5–8 of treatment, after starting at 2.5 mg). Wegovy's equivalent to Mounjaro 5 mg is approximately 0.5 mg. Both are once-weekly injections given via pre-filled pen (Mounjaro's KwikPen or Wegovy's auto-injector).
NHS access to both medications is through specialist tier 3 weight management services — availability varies significantly by region and waiting lists can be substantial. Private access is available through UK-licensed online prescribers following clinical assessment; costs typically range from £129–£320 per month depending on dose. Your GP or prescriber will assess which medication is most suitable based on your health history, comorbidities, and individual circumstances. Try our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and use the BMI calculator to check your starting point.
- 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 5 mg more effective for weight loss than Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (15% body weight) than Wegovy (14.9%), but the difference is modest. Both are effective prescription weight loss options. Individual results vary considerably based on adherence, lifestyle changes, and personal metabolism. Your prescriber can assess which is more suitable for you.
Can you switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official established conversion chart — approximate equivalences exist (e.g., Mounjaro 5 mg ≈ Wegovy 0.5 mg), but any switch requires professional guidance. Your prescriber will assess whether switching is appropriate for your circumstances.
What side effects does Mounjaro 5 mg have?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain — these are typical at the 5 mg dose and often reduce as your body adjusts. Common effects include indigestion, fatigue, and injection site reactions. Serious side effects (severe stomach pain, allergic reactions) require immediate medical attention. Always report side effects to your prescriber.
How do I access Mounjaro or Wegovy in the UK?
On the NHS, both medications are prescribed through specialist tier 3 weight management services following GP referral — availability varies by region and waiting lists can be long. Privately, both are available through UK-licensed online prescribers following a clinical assessment. Regardless of route, both require a prescription and are only suitable if you meet clinical eligibility criteria.
Which injection is better — Mounjaro or Wegovy?
Neither is objectively "better" — suitability depends on your individual health profile, comorbidities, medical history, and how your body responds. Mounjaro's dual mechanism may suit some people; Wegovy's single GLP-1 mechanism suits others. Your GP or prescriber will recommend the most appropriate option following clinical assessment. Results vary between individuals.
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