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 The Long Term Side Effects Of Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK. While clinical trials have shown it to be generally well-tolerated, understanding potential long-term side effects is important before starting treatment. Most side effects are gastrointestinal and tend to improve over time, but some people may experience persistent effects. This guide covers what NHS and clinical data tell us about Mounjaro's long-term safety profile, helping 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.
What Does Long Term Safety Data Show?
Mounjaro received UK MHRA approval with a Black Triangle (▼) status, meaning it's subject to additional monitoring for safety and effectiveness. Clinical trial data from SURMOUNT studies tracked participants over 72 weeks — representing the longest safety evidence currently available.
Key findings from long-term trial data:
- Most common side effects (nausea, diarrhoea, constipation) typically peaked in weeks 4–8 and improved as the body adjusted
- Gastrointestinal symptoms were mostly mild to moderate, with severe cases affecting fewer than 5% of participants
- No new safety concerns emerged beyond the known adverse event profile in the extended trial period
- Participants using the maximum 15 mg Mounjaro KwikPen dose showed similar tolerability to lower doses once stable
However, "long-term" in these trials means under 2 years. Real-world long-term safety (5+ years) remains under ongoing investigation through post-market surveillance. Your GP or prescriber can discuss how NHS monitoring continues even after you start treatment.
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.
Persistent Side Effects And What To Expect
Some people experience side effects that persist beyond the initial adjustment period. These include hair loss (alopecia), fatigue, and continued mild gastrointestinal symptoms. Hair loss has been reported in clinical practice, though it was not formally quantified in trials — it may relate to gradual weight management rather than the medication itself.
Pancreatitis (inflammation of the pancreas) is a serious but rare side effect requiring urgent medical attention. Gallbladder issues, including gallstone formation, have also been observed, particularly with gradual weight management. Contact your GP immediately if you experience severe abdominal pain, persistent vomiting, or signs of an allergic reaction. Before starting Mounjaro, discuss your personal and family medical history with your prescriber, especially any history of thyroid problems, pancreatitis, or gallbladder disease. Use our free GLP-1 weight loss calculator to understand projected outcomes and discuss realistic expectations with your healthcare team.
- 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 long-term side effects of Mounjaro different from short-term ones?
Most long-term side effects are extensions of short-term ones — particularly gastrointestinal symptoms. However, hair loss and fatigue may emerge or persist over months. The SURMOUNT trials showed side effect profiles remained stable beyond 8 weeks. Your GP can provide individualised monitoring based on your specific risk factors.
How long does Mounjaro stay in your system after stopping?
Tirzepatide has a half-life of about 5 days, meaning half the dose is eliminated in that timeframe. Most people clear the medication within 3–4 weeks of stopping. Side effects typically resolve within days to weeks after discontinuation, though weight regain may occur.
Can Mounjaro cause permanent damage to the pancreas?
Pancreatitis risk is rare but serious. Clinical trials did not show permanent pancreatic damage in participants who experienced pancreatitis and discontinued the medication. However, anyone with a personal or family history of pancreatitis should discuss risk with their GP before starting Mounjaro.
Does the NHS monitor people on Mounjaro long-term?
Yes. Mounjaro is prescribed through NHS tier 3 specialist weight management services or privately. Either route requires regular follow-up — typically every 4–12 weeks. Your GP should monitor blood pressure, weight, and any side effects. The MHRA's Black Triangle status means safety data is actively collected.
What should I do if I develop side effects months into Mounjaro treatment?
Report any new or worsening side effects to your GP or prescriber immediately. Do not stop the medication without guidance. Your dose may be adjusted, or — in rare cases — the medication discontinued. Keeping a progress tracker (like the free one on this site) helps document when symptoms begin, supporting your healthcare discussion.
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.