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 Drug Class Is Mounjaro?
Mounjaro (tirzepatide) belongs to a unique drug class called dual GIP and GLP-1 receptor agonists — making it different from other weight management medications available in the UK. Understanding its drug class helps explain how it works and why it may be prescribed through NHS specialist services or private prescribing. This guide covers Mounjaro's classification, mechanism of action, and UK eligibility criteria in straightforward terms.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mounjaro's Drug Class and How It Works
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — the first medication in this combined class to be approved for weight management in the UK. This dual mechanism is what distinguishes it from earlier GLP-1 only medications like Wegovy (semaglutide). GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are natural hormones your gut produces after eating. By activating both pathways, Mounjaro may help regulate appetite more effectively than single-pathway medications.
The drug works by:
- Reducing hunger signals to the brain
- Increasing feelings of fullness after smaller meals
- Slowing how quickly food leaves your stomach (gastric emptying)
- Supporting better blood sugar regulation and fat utilisation
Mounjaro is administered as a once-weekly KwikPen injection available in doses from 2.5 mg to 15 mg. Clinical trials (SURMOUNT-1) showed that participants using Mounjaro achieved average weight loss of 15–21% of body weight over 72 weeks — though individual results vary significantly and depend on diet, activity level, and personal factors. Use our GLP-1 weight loss calculator above to explore potential outcomes at different doses based on your current weight.
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 Drug Class and NHS UK Prescribing
In the UK, Mounjaro is licensed for weight management and available through NHS tier 3 specialist weight management services following referral from your GP, or through private prescribing after an online clinical assessment. The MHRA (Medicines and Healthcare products Regulatory Authority) approved tirzepatide as a prescription-only medicine with standard regulatory status. NHS access varies by region, and waiting times can be substantial — some areas have waiting lists of several months or longer.
To be eligible for Mounjaro through NHS specialist services, you typically need a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (from BMI 27.5). Your GP can refer you to your local tier 3 service for assessment. Private prescribing allows access without NHS referral, though costs apply.
- 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.
How is Mounjaro different from Wegovy in terms of drug class?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, activating two hormone pathways. Wegovy (semaglutide) is a GLP-1 only agonist, activating one pathway. This dual mechanism in Mounjaro may contribute to greater average weight loss in clinical trials, though both are effective and individual results vary.
Is Mounjaro the same as insulin?
No. Mounjaro is not insulin and does not work like insulin. It is a GIP/GLP-1 receptor agonist that works via different hormone pathways. People with type 2 diabetes taking Mounjaro may need adjustment of other diabetes medications — always inform your prescriber of all current treatments.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is available through NHS tier 3 specialist weight management services following GP referral and clinical assessment. However, availability and waiting times vary significantly by region. Private prescribing is also available if you prefer not to wait or are not eligible for NHS services.
What does it mean that Mounjaro has a "Black Triangle" status?
Black Triangle (▼) status means Mounjaro is subject to additional MHRA monitoring for safety. This is standard for newer medicines and does not mean the medication is unsafe — it simply means the regulatory authority is actively monitoring for any emerging safety signals.
How quickly does Mounjaro reach its maximum effect?
Mounjaro is titrated (increased gradually) over 20+ weeks from a starting dose of 2.5 mg up to the maintenance dose (typically 10–15 mg). The gradual increase allows your body to adjust and helps minimise side effects. Maximum benefit is usually seen after several weeks at your target dose.
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.