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
What Are Mounjaro Jabs?
Mounjaro jabs are prescription-only weekly injections containing tirzepatide, a dual GIP and GLP-1 receptor agonist licensed in the UK for weight management. These injections may help reduce appetite and support weight loss when used alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Mounjaro is delivered via a pre-filled KwikPen device and requires a clinical assessment before prescription. It's important to understand how it works, who can access it, and what to expect before starting treatment.
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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 Mounjaro Jabs Work and UK Eligibility
Mechanism: Mounjaro jabs work differently from other weight loss injections like Wegovy (semaglutide). While Wegovy is a single GLP-1 receptor agonist, Mounjaro activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual action may help regulate appetite more effectively, reduce food cravings, and promote feelings of fullness after smaller meals.
UK Eligibility: Mounjaro jabs may be prescribed to UK adults with:
- BMI of 30 kg/m² or above (obesity), or
- BMI of 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply due to higher health risks at lower weights
Your GP or a licensed prescriber will assess whether Mounjaro jabs are suitable for you individually.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Mounjaro Doses, Side Effects, and Expected Results
Dosing: Mounjaro jabs start at 2.5 mg weekly and increase gradually to a maximum of 15 mg. Each dose is held for at least 4 weeks before escalation. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, though individual results vary significantly. Results depend on diet, activity level, and personal metabolism.
Common side effects: Nausea, diarrhoea, vomiting, constipation, and stomach pain are very common, especially at higher doses. These typically improve over time. Try our free GLP-1 weight loss calculator to project potential outcomes at different doses, or use our BMI calculator to understand your current health category.
- 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.
Are Mounjaro jabs the same as Ozempic?
No. Both Mounjaro (tirzepatide) and Ozempic contain semaglutide, but they work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Ozempic is a single GLP-1 agonist designed for type 2 diabetes. Ozempic is not licensed for weight loss in the UK — only Wegovy is the licensed semaglutide weight loss version.
How quickly will I lose weight with Mounjaro jabs?
The NHS recommends losing 0.5–1 kg per week for sustainable results. Mounjaro clinical trials showed average weight loss of 15–21% over 72 weeks alongside diet and activity changes. However, individual results vary significantly — some people lose more, some less. Weight loss depends on your starting weight, adherence to lifestyle changes, and personal metabolism.
Can I get Mounjaro jabs on the NHS in the UK?
Mounjaro is available through NHS specialist weight management services (tier 3 and 4). Access requires referral from your GP and assessment by a specialist team. Availability and waiting times vary significantly by region. Private prescriptions are also available through licensed online prescribers following a clinical assessment.
What happens if I miss a Mounjaro jab dose?
If you miss a dose within 4 days, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next one on your regular day. Never take a double dose. Always contact your prescriber or pharmacist if you're unsure.
Do Mounjaro jabs work better than Wegovy for weight loss?
Clinical trial data shows Mounjaro (tirzepatide) achieved slightly higher average weight loss than Wegovy (semaglutide) — around 20.9% versus 14.9% at maximum doses. However, individual responses vary greatly, and both are effective. The best choice depends on your personal health profile, medical history, and prescriber assessment — not on average trial data alone.
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.