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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Mounjaro Long Term Use — Evidence and Safety
Mounjaro (tirzepatide) is a prescription-only weight management injection that's designed for ongoing use. Current evidence from clinical trials suggests it may be safe and effective for long-term treatment, though studies are still ongoing. In the UK, GPs and specialist services prescribe Mounjaro for sustained weight management, often alongside lifestyle changes. This guide explains what we know about extended use, how long people typically continue treatment, and what the evidence shows about safety and effectiveness over time.
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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 Mounjaro Treatment Look Like?
Long-term Mounjaro use typically involves continuing once-weekly injections at your maintenance dose (usually 10mg, 12.5mg, or 15mg) for as long as the medication remains effective and well-tolerated. The SURMOUNT clinical trials, which ran for up to 72 weeks, showed sustained weight loss at stable doses — but real-world long-term use often extends beyond this timeframe.
In UK clinical practice, patients may continue Mounjaro for 12 months or longer if weight loss continues and side effects remain manageable. Your prescriber will review your progress regularly using your free progress tracker or clinical notes to assess whether the medication is still working for you.
- Maintenance phase typically begins at week 16–20 after dose escalation
- Weight loss plateaus may occur after 6–12 months — this is normal
- Your GP or specialist can adjust your dose or review your treatment plan at any time
- Regular blood pressure and metabolic monitoring is recommended
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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.
Safety and Side Effects Over Extended Periods
Extended safety data for Mounjaro is still being gathered through post-marketing surveillance and ongoing clinical studies. The SURMOUNT trials showed that most side effects (nausea, diarrhoea, constipation) occurred early in treatment and often improved over time. Some patients experience persistent gastrointestinal effects even at maintenance dose.
Important considerations for long-term use include: the risk of pancreatitis (extremely rare), gallbladder complications in susceptible individuals, and potential medication interactions with other prescriptions. Your prescriber will monitor you through regular check-ups. If you experience severe abdominal pain or signs of pancreatitis at any point, seek urgent medical attention. Always inform your GP of new symptoms.
- 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.
Can you stay on Mounjaro indefinitely?
There's no absolute time limit, but long-term use requires ongoing clinical assessment. Your prescriber will review whether Mounjaro is still working and safe for you at regular intervals. If weight loss stops or side effects become intolerable, your treatment plan may change.
What happens to weight loss if you stay on Mounjaro long term?
Weight loss typically stabilises after 6–12 months at your maintenance dose. Some people maintain their loss indefinitely; others experience gradual regain if lifestyle habits change. Individual responses vary significantly — use our GLP-1 weight loss calculator to estimate potential long-term outcomes.
Are there new side effects that emerge after months on Mounjaro?
Most side effects occur in the first 4–8 weeks. However, long-term tolerability data is still limited. Report any new or worsening symptoms to your GP immediately, including persistent nausea, vision changes, or unusual abdominal pain.
How does long-term Mounjaro compare to Wegovy long term?
Both are GLP-1-based injections (Mounjaro is dual GIP/GLP-1) with similar safety profiles in trials. Mounjaro showed numerically higher weight loss in SURMOUNT trials (~20.9% at 15mg) versus Wegovy in STEP trials (~14.9% at 2.4mg), but long-term real-world outcomes are comparable. Individual response varies.
What happens when you stop Mounjaro after long-term use?
Weight regain typically begins within weeks of stopping, as appetite hormones normalise. Most people return toward their baseline weight within 6–12 months if lifestyle changes aren't maintained. Your prescriber can discuss transition strategies before stopping treatment.
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.