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 12.5mg — What You Need to Know
Mounjaro 12.5mg is the second-highest maintenance dose of tirzepatide, a prescription-only GLP-1 and GLP-1 receptor agonist licensed in the UK for weight management in adults. This dose is typically reached after 16–20 weeks of gradual dose escalation, following a clinical assessment by a licensed prescriber. Most users do not require the 12.5mg dose—many achieve their weight loss goals at lower doses—but it is available for those who need greater appetite suppression or have shown a slower response at earlier doses.
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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.
Mounjaro 12.5mg Dosing Schedule and Escalation Path
Mounjaro 12.5mg is reached gradually, not as a starting dose. The typical escalation path is: 2.5mg (weeks 1–4), 5mg (weeks 5–8), 7.5mg (weeks 9–12), 10mg (weeks 13–16), and 12.5mg (weeks 17–20). Each dose is a once-weekly injection delivered via a pre-filled Mounjaro KwikPen. Your prescriber will assess your progress at each stage before increasing. If you experience significant side effects—such as persistent nausea or vomiting—your prescriber may recommend staying at a lower dose rather than continuing escalation. You must wait at least 4 weeks at each dose level before moving up. Some patients stay on 10mg or 15mg depending on individual response and tolerability.
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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.
12.5mg Weight Loss Expectations and Individual Variation
Clinical trial data shows that Mounjaro users on 12.5mg lose an average of approximately 19–21% of their body weight over 72 weeks—though individual results vary significantly. Some people lose more, others less. Use our free GLP-1 weight loss calculator above to estimate potential weight loss at different doses based on your starting weight. Weight loss at this dose typically requires a reduced-calorie diet and increased physical activity alongside the injection. The 12.5mg dose is not a "clinically supported solution"—it is a tool that works best when combined with lifestyle changes. If you have not lost at least 4% of your body weight by 12 weeks on the dose, your prescriber will discuss whether to continue or adjust your approach.
- 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 is the difference between Mounjaro 12.5mg and Mounjaro 15mg?
Mounjaro 15mg is the maximum licensed dose. The difference between 12.5mg and 15mg is typically modest in terms of additional weight loss. Many people achieve their target weight loss at 12.5mg. Escalation to 15mg is decided on an individual basis by your prescriber, usually only if needed for further weight loss or diabetes control.
Can I skip the dose escalation and start at 12.5mg?
No. Mounjaro must be started at 2.5mg and escalated gradually. Starting at a higher dose increases the risk of severe side effects, particularly nausea, vomiting, and gastrointestinal distress. Gradual escalation allows your body to adapt and helps identify the lowest effective dose for you.
Is Mounjaro 12.5mg available on the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services in some regions, but availability varies significantly by area and waiting lists can be very long. Private prescribing through online clinics is more widely available. Either way, you need a prescription from a licensed UK prescriber and a clinical assessment before starting.
What if I miss a 12.5mg injection?
If you miss an injection, take it within 4 days of the scheduled date and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on the usual day. Never take a double dose. The minimum time between doses is 72 hours.
Does Mounjaro 12.5mg vs Wegovy matter if I want weight loss?
Mounjaro is a dual GIP/GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Both are licensed for UK weight management. Average weight loss is similar (around 15–21% with Mounjaro, around 15% with Wegovy), but individual response varies. Your prescriber will advise which is most suitable based on your health profile and eligibility.
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.