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 Is Terzipatide and How Does It Work?
Terzipatide is a prescription-only weight management injection licensed in the UK under the brand name Mounjaro. It works differently from other weight loss medications because it activates two natural hormone pathways — GIP and GLP-1 — which helps regulate appetite and support feeling fuller after meals. This dual mechanism makes it unique among UK-licensed weight management options. If you're wondering whether terzipatide might be right for you, understanding how it works and what eligibility criteria apply is the first step towards exploring your options with your GP or a licensed prescriber.
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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.
How Terzipatide Works and What to Expect
Terzipatide activates two hormone pathways simultaneously:
- GIP (glucose-dependent insulinotropic polypeptide): Helps regulate how your body processes food and may reduce appetite signals
- GLP-1 (glucagon-like peptide-1): Signals fullness to the brain, slows stomach emptying, and supports blood sugar stability
This dual action is what distinguishes terzipatide from single-mechanism GLP-1 medications like semaglutide (Wegovy). In clinical trials, terzipatide helped participants lose an average of 15–21% of their body weight over 72 weeks when combined with reduced-calorie diet and increased physical activity — though individual results vary significantly. You can explore projected weight loss outcomes using our GLP-1 weight loss calculator. Side effects are common in early weeks (nausea, diarrhoea, constipation) but often improve as your body adjusts to the medication.
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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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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
UK Eligibility, Doses, and How to Access Terzipatide
You may be eligible for terzipatide (Mounjaro) in the UK if:
- BMI of 30 kg/m² or above, or
- BMI of 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease)
- Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights
Terzipatide is dosed weekly, starting at 2.5 mg and escalating to a maximum of 15 mg. Access is available through NHS specialist weight management services (tier 3) or private online prescribing following clinical assessment. Check your personal BMI using our free BMI calculator to understand where you sit on the UK health scale.
- 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.
Is terzipatide the same as Mounjaro?
Yes. Terzipatide is the active ingredient; Mounjaro is the UK brand name for the injection. You'll see both names used interchangeably in UK healthcare. When your prescriber or pharmacist mentions either term, they're referring to the same medication.
How much weight can I expect to lose with terzipatide?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, but individual results vary significantly. Weight loss depends on your starting weight, adherence to reduced-calorie diet, physical activity, and how your body responds. Your GP can give you personalised estimates.
Is terzipatide available on the NHS in the UK?
Yes, terzipatide is approved for NHS use through specialist tier 3 weight management services. Access varies by region and local availability, and waiting lists can be lengthy. Private prescribing through GPhC-registered pharmacies is also available without NHS referral.
What's the difference between terzipatide and semaglutide?
Terzipatide (Mounjaro) is a dual GIP+GLP-1 agonist, while semaglutide (Wegovy) is a GLP-1-only agonist. Clinical data suggests terzipatide may produce slightly greater average weight loss, but both are effective. Your prescriber will recommend the most suitable option based on your health profile.
What are the most common side effects of terzipatide?
Nausea, diarrhoea, vomiting, and constipation are very common, especially in the first 4–8 weeks. These often improve as your body adjusts. Seek immediate medical attention for severe stomach pain (possible pancreatitis), serious allergic reactions, or gallbladder symptoms. Always report any concerns to your GP or prescriber.
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.