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
Are Mounjaro Injections Safe in the UK?
Yes, Mounjaro (tirzepatide) injections are approved as safe for weight management in the UK, with ongoing monitoring by the MHRA. Like all prescription medicines, Mounjaro has a known safety profile with common and manageable side effects. Safety depends on proper medical assessment before starting, correct dose titration, and following your prescriber's guidance. This guide explains what the evidence shows about Mounjaro safety, how to minimise risks, and what to expect during treatment. Understanding both benefits and potential side effects helps you make an informed decision with your healthcare provider.
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 Safety Profile and Known Side Effects
Mounjaro has been extensively studied in clinical trials. The SURMOUNT trials demonstrated its safety and effectiveness for weight management across large patient populations. The MHRA approved Mounjaro with ongoing monitoring (Black Triangle ▼ status), meaning safety data is continuously reviewed. Common side effects affect more than 1 in 10 people and include nausea, diarrhoea, vomiting, and constipation — typically occurring in the first few weeks and often improving as your body adjusts. Less common but serious side effects require immediate medical attention, including severe stomach pain (possible pancreatitis), gallbladder problems, serious allergic reactions, and changes in vision. Individual side effect experiences vary significantly. Your prescriber will discuss your personal risk factors and monitor you throughout treatment to ensure safety.
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.
UK Access, Cost, and Private vs NHS Routes
In the UK, Mounjaro is accessed through two main routes. The NHS route involves referral to a tier 3 specialist weight management service, where clinicians assess eligibility and prescribe alongside a reduced-calorie diet and physical activity programme. NHS availability varies significantly by region, and waiting lists can extend several months. The private route uses online consultations with UK-licensed prescribers and dispensing through GPhC-registered pharmacies, typically available within days. Private costs range from approximately £129 to £320 per month depending on your dose. Both routes require a clinical assessment — Mounjaro is prescription-only and not available over the counter. Your GP can advise which route suits your circumstances.
- 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.
What are the most common Mounjaro side effects in the UK?
The most common side effects are nausea, diarrhoea, vomiting, and constipation, affecting more than 1 in 10 people. These typically occur when starting or increasing your dose and often improve within a few days or weeks as your body adjusts. Eating smaller, lighter meals and staying hydrated can help manage these effects. If side effects persist or worsen, contact your prescriber immediately.
Is Mounjaro safe for long-term use?
Yes, Mounjaro is approved for ongoing use when clinically appropriate. The SURMOUNT trials followed participants for over a year, showing sustained safety. However, long-term safety data continues to be collected as more people use it. Your prescriber will regularly assess whether Mounjaro remains suitable for you and monitor your health throughout treatment.
Who should not use Mounjaro injections?
Mounjaro is not suitable for people under 18, those pregnant or breastfeeding, or with allergies to tirzepatide. It's also not recommended for people with a personal or family history of medullary thyroid cancer or severe gastroparesis. Your prescriber will review your medical history and medications to confirm Mounjaro is safe and appropriate for you.
Can I use Mounjaro if I take other medications?
Mounjaro may interact with some medications, particularly oral contraceptives and diabetes medicines. Oral contraceptives may be less effective during Mounjaro treatment — add a barrier method or switch contraception for 4 weeks after starting and after each dose increase. Always tell your prescriber about all medications, supplements, and health conditions before starting Mounjaro.
How does Mounjaro safety compare to Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines approved for UK weight management with similar safety profiles. The main difference is Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist only. Both cause similar common side effects. Your prescriber will assess which is most appropriate based on your individual health circumstances and any contraindications.
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.