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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What to Expect After 3 Months on Mounjaro
After three months on Mounjaro (tirzepatide), most people are in the dose escalation phase, working towards their maintenance dose. By this point, side effects often improve, energy levels typically stabilise, and many people notice meaningful changes in appetite and food preferences. Individual experiences vary significantly depending on your starting dose, how your body responds, and lifestyle changes. This guide explains what typically happens after 12 weeks of Mounjaro treatment in the UK.
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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.
Expected Changes by Week 12 of Mounjaro Treatment
By the three-month mark on Mounjaro, you're likely to have progressed through the initial dose titration schedule. If you started at 2.5 mg, you've typically moved through 5 mg and possibly 7.5 mg doses. At this stage:
- Weight loss progress: Clinical data suggests people typically lose between 5–8% of body weight by week 12, though results vary significantly based on adherence to diet and exercise changes
- Side effects: Initial nausea and digestive changes often begin to improve as your body adjusts to the medication
- Appetite changes: Most people report continued appetite reduction and increased feeling of fullness after eating smaller meals
- Energy levels: Many people report stabilised energy after the initial adjustment period
- Next steps: Your prescriber will assess whether to continue escalating your dose towards 10 mg, 12.5 mg, or 15 mg, depending on your response and tolerance
Use our GLP-1 weight loss calculator to project potential weight loss over your treatment journey, and our progress tracker to log changes week by week.
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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.
Managing Side Effects and Health Changes at 3 Months
By 12 weeks, most people have adapted to Mounjaro's effects. Nausea typically lessens as your digestive system adjusts, though some people continue to experience mild symptoms. Constipation or diarrhoea may persist — staying hydrated and eating smaller, nutrient-dense meals helps. Some people notice changes in how they respond to foods they previously enjoyed, which supports reduced calorie intake naturally.
Monitor your blood sugar and blood pressure if you have type 2 diabetes or hypertension — weight loss may affect medication requirements, so discuss any changes with your GP. Keep tracking your progress using our progress tracker tool to identify patterns and adjust your diet and exercise approach if needed. If you're experiencing severe or persistent side effects, contact your prescriber before your next scheduled dose escalation.
- 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.
How much weight should I have lost after 3 months on Mounjaro?
Clinical trials show an average weight loss of 5–8% of body weight by 12 weeks, but individual results vary significantly. Your weight loss depends on your starting dose progression, dietary adherence, physical activity level, and individual metabolism. Some people lose more, others less. Your prescriber can assess your personal progress.
Will my Mounjaro dose increase at 3 months?
If you're tolerating your current dose well and responding adequately, your prescriber may increase your dose at the 12-week mark. The standard schedule involves increasing every 4 weeks: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg. Your prescriber decides the timing based on your tolerance and response.
Why am I still experiencing nausea at 3 months?
Most people's nausea improves significantly by week 12, but some continue to experience mild symptoms. This is normal and usually lessens with continued treatment. Eating smaller, slower meals and staying hydrated helps. If nausea is severe or affecting your quality of life, discuss this with your prescriber before your next dose increase.
Can I expect more weight loss in months 4–6 compared to months 1–3?
Many people continue to lose weight in months 4–6, particularly as their dose increases and they continue lifestyle changes. However, weight loss rates often plateau slightly as your body adapts. Consistency with diet and exercise remains crucial throughout treatment.
What happens to my appetite if I'm still on a lower dose at 3 months?
If you're still escalating doses (e.g., on 7.5 mg at 12 weeks), appetite suppression continues to strengthen as you move to higher doses. At 3 months, you should notice clear appetite reduction compared to before starting treatment. This effect intensifies with each dose increase, supporting sustained dietary changes.
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.