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 Dosage For Weight Loss — How It Works
Tirzepatide is a prescription-only weight loss injection available in the UK under the brand name Mounjaro. The medication works as a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to help regulate appetite and support feeling fuller after meals. Tirzepatide dosage starts low and increases gradually over several weeks, allowing your body to adjust. This guide explains the complete dosage schedule, how escalation works, and what clinical trials have shown about weight loss outcomes. Always consult your GP or a licensed prescriber to determine if tirzepatide is suitable for your individual health situation.
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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.
Understanding Tirzepatide Dosage Schedule
Tirzepatide is administered as a once-weekly injection using the Mounjaro KwikPen device. The dosage starts at 2.5 mg and increases gradually in a step-wise pattern over several months.
- Weeks 1–4: 2.5 mg (starting/adjustment dose)
- Weeks 5–8: 5 mg (first maintenance dose)
- Weeks 9–12: 7.5 mg (escalation if needed)
- Weeks 13–16: 10 mg (escalation if needed)
- Weeks 17–20: 12.5 mg (escalation if needed)
- Weeks 21+: 15 mg (maximum dose)
You must stay on each dose for a minimum of 4 weeks before increasing. Each KwikPen contains 4 doses (4 weeks of treatment). Your prescriber will assess your progress at each escalation point and determine whether to increase based on your individual response and tolerance.
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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.
Weight Loss Results and Clinical Evidence
Clinical trials (SURMOUNT-1) showed that tirzepatide helped participants lose an average of 15–21% of their body weight over 72 weeks, depending on the dose — though individual results vary significantly. At the 15 mg dose, average weight loss was approximately 20.9% of body weight. These results were achieved alongside a reduced-calorie diet and increased physical activity. Use our GLP-1 weight loss calculator above to estimate potential weight loss projections at different tirzepatide doses based on your current weight. Most people experience noticeable effects within 4–8 weeks as the dose escalates.
- 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?
The starting dose is 2.5 mg, taken as a once-weekly injection. You remain on this dose for 4 weeks to allow your body to adjust. This lower starting dose helps minimise side effects as your system acclimatises to the medication. Your prescriber will then assess whether to escalate to 5 mg based on your response and tolerance.
Can I skip doses or increase tirzepatide faster?
No. You must take tirzepatide exactly as prescribed, once per week. Never skip doses or try to increase faster than your prescriber recommends. The step-wise escalation schedule exists to help your body adjust safely. If you miss a dose by more than 4 days, skip it and continue your normal schedule — never take a double dose.
What is the maximum tirzepatide dose?
The maximum dose is 15 mg per week. Not everyone requires the maximum dose — your prescriber will assess what works best for you. Some people achieve their weight loss goals at lower doses like 10 mg or 12.5 mg. The appropriate dose depends on your individual health, tolerance, and response to treatment.
How long does tirzepatide take to work for weight loss?
Most people notice reduced appetite and weight loss effects within 4–8 weeks as doses escalate. However, significant weight loss typically becomes visible around weeks 8–12. Patience is important — the medication works gradually alongside lifestyle changes. Calculate your BMI and track your progress using our free progress tracker to monitor results over time.
Is tirzepatide the same as semaglutide (Wegovy)?
No. Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways. Semaglutide (Wegovy) is a GLP-1-only agonist. Both are licensed for weight loss in the UK, but tirzepatide's dual mechanism may offer different results. Clinical trials showed tirzepatide produced slightly higher average weight loss than semaglutide, though individual outcomes vary.
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.