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
Is Monjaro Safe in the UK?
Yes, Monjaro (tirzepatide) is approved as safe for weight management in UK adults by the MHRA and is prescribed through NHS specialist services and private clinics. Like all prescription medications, it carries potential side effects and requires clinical assessment before use. Understanding the safety profile, eligibility criteria, and how it works as a GLP-1 receptor agonist helps you make an informed decision about whether this weekly weight loss injection is right for you.
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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.
MHRA Approval and Clinical Evidence
Monjaro received MHRA approval in December 2023 for weight management in UK adults. The medicine is subject to additional monitoring (Black Triangle ▼ status), meaning the MHRA continues to closely track safety data. The approval was based on the SURMOUNT clinical trials, which demonstrated that tirzepatide helped participants lose an average of 15–21% of their body weight over 72 weeks, depending on dose.
The MHRA's approval means Monjaro meets UK safety and efficacy standards. However, it is not suitable for everyone. You must have a BMI of 30 kg/m² or above, or BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, heart disease, or sleep apnoea). Lower BMI thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults due to higher disease risk at lower weights.
Monjaro is a dual GIP and GLP-1 receptor agonist—meaning it activates two hormone pathways to regulate appetite and metabolism, making it distinct from single GLP-1 medications like Wegovy (semaglutide).
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.
Common Side Effects and When to Seek Help
The most common side effects of Monjaro are nausea, diarrhoea, vomiting, and constipation—reported in over 1 in 10 people. These typically improve over time as your body adjusts. Stomach pain, indigestion, headache, fatigue, and injection site reactions are also frequently reported.
Seek urgent medical attention if you experience severe, persistent abdominal pain (possible pancreatitis), serious allergic reactions, gallbladder symptoms, or unexplained changes in vision. Before starting, inform your prescriber of all medications you take—Monjaro can affect how oral contraceptives and some diabetes medications are absorbed.
Use our GLP-1 weight loss calculator to estimate potential outcomes, and our BMI calculator to check your starting point before discussing Monjaro eligibility with your GP.
- 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 Monjaro safe for long-term use in the UK?
Monjaro is licensed for long-term weight management in UK adults. MHRA monitoring continues through its Black Triangle status. Long-term safety data from extended trials is positive, but your prescriber will monitor your health regularly. Safety depends on proper dose titration, adherence to injection technique, and regular check-ups.
Can I get Monjaro on the NHS in the UK?
Yes, Monjaro is available through NHS specialist tier 3 weight management services following referral from your GP. However, NHS availability varies significantly by region and waiting lists can be lengthy. Private online prescribing is also available through UK-registered prescribers after clinical assessment, with costs typically £150–£320 per month depending on dose.
What makes Monjaro different from other weight loss injections like Wegovy?
Monjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Monjaro achieved slightly higher average weight loss (20.9% at 15mg vs 14.9% for Wegovy at 2.4mg). Both are prescription-only and require clinical assessment. Individual results vary significantly.
What happens if I stop taking Monjaro—will I regain weight?
Weight regain can occur after stopping Monjaro, as appetite hormones return to baseline. However, if lifestyle changes (diet and exercise) are maintained, weight loss may be partially sustained. Your prescriber can discuss long-term management strategies and whether continued treatment is appropriate for you.
Are there any drug interactions I should know about with Monjaro?
Monjaro can reduce absorption of oral medications, including oral contraceptives. Women taking the pill should use additional contraception for 4 weeks after starting and after each dose increase. Diabetes medications may need adjustment. Always inform your prescriber and pharmacist of all medications and supplements you take.
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.