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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Is Mounjaro Safe for Weight Management?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with health conditions. Like all medications, Mounjaro has potential side effects and isn't suitable for everyone. Understanding its safety profile, how it works, and who can safely use it is essential before considering this treatment. This guide covers what you need to know about Mounjaro safety based on clinical evidence and UK healthcare guidance. Always consult your GP or a licensed prescriber for personalised advice about whether this medication 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.
How Mounjaro Works and What Clinical Trials Show
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to help regulate appetite and support weight loss. Clinical trials (SURMOUNT-1) showed that tirzepatide helped participants lose an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. These results were achieved alongside a reduced-calorie diet and increased physical activity — the medication alone is not a substitute for lifestyle changes.
In clinical trials, the most common side effects were gastrointestinal, including nausea, diarrhoea, vomiting, and constipation. Most side effects were mild to moderate and decreased over time as the body adjusted. However, some people experienced severe nausea or other complications that required stopping treatment.
- Mounjaro is given as a once-weekly injection (via KwikPen)
- Doses start at 2.5 mg and escalate up to 15 mg maximum
- Each dose is held for a minimum of 4 weeks before increasing
- Weight loss is not assured — it depends on individual metabolism and adherence to diet and exercise
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.
Who Can Safely Use Mounjaro and Important Precautions
Mounjaro may be prescribed to UK adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at lower BMI thresholds due to higher health risks at lower weights.
Mounjaro is not suitable for:
- Under 18 years old
- Pregnant or planning pregnancy
- Breastfeeding
- Anyone with a history of thyroid cancer or MEN2
- People with severe kidney or liver disease
- Those with a personal or family history of medullary thyroid carcinoma
A prescriber will assess your full medical history before prescription. If you experience severe stomach pain, persistent vomiting, or signs of allergic reaction, seek medical attention immediately.
- 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 serious side effects of Mounjaro?
The most serious potential side effects are rare but include pancreatitis (severe stomach pain), gallbladder problems, and diabetic retinopathy complications in people with existing diabetes. Severe allergic reactions are very rare. If you experience severe abdominal pain, persistent vomiting, or difficulty breathing, seek immediate medical attention and contact your GP or NHS 111.
Is Mounjaro safe for people with type 2 diabetes?
Yes, Mounjaro can be prescribed to people with type 2 diabetes for weight management. However, if you're already taking diabetes medications like insulin or sulphonylureas, your prescriber may need to adjust doses to prevent low blood sugar. Always inform your prescriber of all current medications and health conditions.
How does Mounjaro safety compare to Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are licensed weight management medications in the UK with similar safety profiles. Mounjaro is a dual GIP/GLP-1 agonist while Wegovy is a single GLP-1 agonist. Clinical trials show similar side effect patterns. Safety depends on individual factors — your prescriber will assess which is more appropriate for you.
Can I use our GLP-1 weight loss calculator to check if I'm eligible for Mounjaro?
Our weight loss calculator can give you a personalised estimate of potential results at different doses, which may help you understand whether this medication could be relevant for your situation. However, eligibility for Mounjaro requires a clinical assessment by a licensed prescriber, who will review your medical history, current medications, and health conditions. Use the calculator as an informational tool, then discuss your situation with your GP.
What should I do if I experience side effects while taking Mounjaro?
Most side effects (nausea, diarrhoea, constipation) are mild and improve over time. Take Mounjaro at consistent times, eat smaller meals, and stay hydrated. If side effects are severe or persistent after 2–3 weeks, contact your prescriber — they may adjust your dose or recommend stopping treatment. Never stop taking Mounjaro without medical guidance.
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.