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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When Should You Increase Your Mounjaro Dosage?
Mounjaro dosage increases follow a structured schedule set by your prescriber, not your own decision. The standard UK approach involves increasing the dose every 4 weeks, starting at 2.5 mg and escalating up to a maximum of 15 mg once weekly. Understanding when and why your prescriber might increase your tirzepatide dose — and how this compares to Wegovy's approach — can help you get the most from your weight management treatment. This guide covers the key differences between the two weight loss medications and what to expect during your treatment journey.
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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 vs Wegovy: Dosage Schedules and Titration
Mounjaro (tirzepatide) and Wegovy (semaglutide) use different dosage schedules because they have different mechanisms of action. Mounjaro is a dual GIP and GLP-1 receptor agonist, allowing for higher therapeutic doses, whilst Wegovy is a GLP-1 agonist only. Mounjaro's standard titration increases every 4 weeks: 2.5 mg (weeks 1–4), 5 mg (weeks 5–8), 7.5 mg (weeks 9–12), 10 mg (weeks 13–16), 12.5 mg (weeks 17–20), and 15 mg (week 21 onwards). Wegovy's schedule is longer: 0.25 mg (weeks 1–4), 0.5 mg (weeks 5–8), 1 mg (weeks 9–12), 1.7 mg (weeks 13–16), and 2.4 mg (week 17 onwards). Clinical trials showed that Mounjaro achieved average weight loss of approximately 15–21% of body weight, whilst Wegovy achieved around 15% — though individual results vary considerably. Your prescriber will assess whether you're tolerating each dose before recommending an increase, particularly if you're experiencing nausea or other gastrointestinal side effects. Using our GLP-1 weight loss calculator can help you understand potential weight loss projections at different dose levels based on clinical trial data.
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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.
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What Your Prescriber Assesses Before a Dose Increase
Your prescriber won't automatically increase your Mounjaro dose — they'll assess several factors first. These include how well you're tolerating the current dose, whether you're experiencing side effects (particularly nausea, diarrhoea, or vomiting), your weight loss progress, and any underlying health conditions such as previous pancreatitis or diabetic retinopathy. If you're experiencing significant side effects, your prescriber may delay increasing the dose or keep you at a maintenance dose rather than escalating further. It's important to be honest about side effects during your reviews — they typically improve over time as your body adapts, but your prescriber needs this information to make the right decision for you. Both Mounjaro and Wegovy require a UK prescription and ongoing clinical assessment; neither medication is adjusted without professional guidance. Tracking your weight loss progress using our free progress tracker can help you provide accurate information at your prescriber appointments.
- 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 I ask my prescriber to increase my Mounjaro dose faster than every 4 weeks?
No. The standard UK guidance is to increase every 4 weeks minimum to allow your body to adapt and to monitor for side effects safely. Your prescriber will follow this schedule and may delay increases if you're experiencing significant gastrointestinal symptoms.
How does Mounjaro's dosage schedule compare to Wegovy's?
Mounjaro increases every 4 weeks and reaches 15 mg maximum, whilst Wegovy increases every 4 weeks but reaches only 2.4 mg maximum. The higher Mounjaro doses are possible because tirzepatide works on two hormone pathways (GIP and GLP-1), whereas semaglutide works on one (GLP-1 only).
What if I'm not losing weight on my current Mounjaro dose?
Your prescriber will assess whether a dose increase is appropriate. However, weight loss depends on multiple factors including diet, activity level, underlying health conditions, and individual metabolism. Your prescriber may also recommend lifestyle support before increasing the dose.
Will I experience more side effects if my Mounjaro dose increases?
Many people experience mild side effects when increasing doses, typically nausea or changes in bowel habits. These usually settle within a few days. Always report side effects to your prescriber — they can advise whether to continue or adjust the dose.
What's the maximum Mounjaro dose, and when is it reached?
The maximum Mounjaro dose is 15 mg once weekly, typically reached by week 21 of treatment. Not everyone needs or tolerates the maximum dose — your prescriber will find the optimal dose for you based on efficacy and tolerability.
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.