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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Tirzepatide Doses For Weight Loss — How It Compares
Tirzepatide is a prescription weight loss injection available in the UK as Mounjaro. Understanding its dosing schedule and how it compares to other GLP-1 receptor agonist medications can help you make informed health decisions. This guide explains tirzepatide dosing for weight loss, the mechanism behind it, and how it differs from semaglutide (Wegovy). Both are prescription-only medicines requiring clinical assessment before use. Use our GLP-1 weight loss calculator to explore potential outcomes at different dose levels.
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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.
Tirzepatide vs Semaglutide Dosing — Clinical Trial Data
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways for appetite regulation and blood sugar control. It starts at 2.5 mg weekly, escalating by 2.5 mg increments every four weeks up to a maximum of 15 mg weekly. In the SURMOUNT-1 clinical trial, participants on 15 mg tirzepatide achieved average weight loss of approximately 20.9% body weight over 72 weeks alongside reduced-calorie diet and increased physical activity.
Semaglutide (Wegovy) is a GLP-1 receptor agonist only — activating a single hormone pathway. It starts at 0.25 mg weekly, escalating to a maximum of 2.4 mg weekly. In the STEP-1 trial, participants on 2.4 mg semaglutide achieved average weight loss of approximately 14.9% body weight over 68 weeks with the same lifestyle support.
The key difference: tirzepatide's dual mechanism may offer greater weight loss potential in clinical settings, though individual results vary significantly. A prescriber will assess which medication is suitable for your specific health profile.
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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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Which Dose Is Right For You? — Individual Assessment
Both tirzepatide and semaglutide require a clinical assessment before prescription. A licensed prescriber will evaluate your BMI, existing health conditions, medications, and medical history to determine eligibility and the appropriate starting dose. Neither medication is suitable for everyone — those with personal or family history of medullary thyroid cancer, multiple endocrine neoplasia type 2, or severe gastroparesis are typically not candidates.
Doses are escalated gradually over weeks or months, with your prescriber monitoring your response and tolerability. Some people reach effective weight loss at lower doses (e.g. 5 mg tirzepatide), whilst others progress to the maximum. Access in the UK is through NHS specialist weight management services (with potential waiting lists) or private online prescribing following clinical assessment. Your GP can discuss which route is appropriate for you.
- 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 starting dose of tirzepatide for weight loss?
The starting dose of tirzepatide (Mounjaro) is 2.5 mg once weekly. This is adjusted upward by 2.5 mg increments every four weeks, with most people reaching 5–15 mg depending on response and tolerability.
How does tirzepatide differ from semaglutide (Wegovy)?
Tirzepatide is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. Semaglutide is a GLP-1 agonist only. Clinical trials suggest tirzepatide may produce greater average weight loss (20.9% vs 14.9%), though individual results vary considerably.
Can I switch between tirzepatide and semaglutide?
Switching between medications is possible but must be managed by your prescriber. There is no official established conversion between doses — your prescriber will assess the appropriate dose and monitor your response during any transition.
Is tirzepatide available on the NHS in the UK?
Yes, tirzepatide (Mounjaro) is approved by NICE for NHS specialist weight management services. However, NHS availability varies by region, and waiting lists can be lengthy. It is also available through private online prescribing with a clinical assessment.
What happens if I miss a tirzepatide dose?
If you miss a dose, take it within four days of the missed date, then continue your normal weekly schedule. If more than four days have passed, skip the missed dose and take your next dose on the regular day. Never take a double dose.
Ready to take control of your weight loss journey?
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