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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Weight Loss Jab Retatrutide — What You Need to Know
Retatrutide is a newer weight loss injection currently in development that works similarly to other GLP-1 medications available in the UK. Unlike prescription weight loss injections already licensed here such as Mounjaro and Wegovy, retatrutide remains in clinical trials and is not yet approved by UK regulators. This guide explains how it works, current evidence, and what options are available to you now for prescription weight loss medication through NHS weight loss services or private prescribing.
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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 Retatrutide Works and Current Status
Retatrutide is a triple GIP, GLP-1, and glucagon receptor agonist — meaning it activates three natural hormone pathways rather than one or two. This triple mechanism may help regulate appetite more effectively than currently available medications. However, it remains in clinical trial phases and is not yet licensed in the UK by the MHRA.
Currently available licensed alternatives:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 agonist, licensed for weight management in UK adults with BMI ≥30 or BMI 27–29.9 with health conditions
- Wegovy (semaglutide) — GLP-1 agonist only, licensed and available through NHS specialist services or private prescribing
- Saxenda (liraglutide) — GLP-1 agonist, daily injection option
If you're interested in weight loss medication now, your GP can refer you to NHS tier 3 specialist weight management services, or you can access prescription treatment through private online prescribing following a clinical assessment.
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No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Eligibility for Weight Loss Medication in the UK Now
To access prescription weight management medication in the UK today, you typically need a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights.
Calculate your personal BMI using our free BMI calculator above to see where you fall. If you're eligible, ask your GP about referral to NHS specialist weight loss services, or explore private options through UK-licensed prescribers. A clinical assessment will determine which medication is most suitable for your individual health situation.
- 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 retatrutide available in the UK now?
No. Retatrutide is still in clinical development and has not yet been approved by UK regulators (MHRA). You cannot currently access it on the NHS or through private UK prescribers. Licensed alternatives like Mounjaro and Wegovy are available now for eligible adults.
How does retatrutide differ from Mounjaro and Wegovy?
Retatrutide activates three hormone pathways (GIP, GLP-1, and glucagon), while Mounjaro activates two (GIP and GLP-1) and Wegovy activates one (GLP-1). This triple mechanism may offer different weight loss outcomes, but clinical trials are still ongoing.
When might retatrutide become available in the UK?
Timeline for MHRA approval is uncertain. Once Phase 3 trials are complete and data submitted to regulators, approval typically takes several months to years. Your GP can discuss currently available options while you wait.
What weight loss results did retatrutide show in trials?
Early clinical trial data suggests retatrutide may produce weight loss results comparable to or exceeding current GLP-1 medications, but final Phase 3 data has not yet been published. Individual results always vary significantly regardless of medication type.
What should I do if I want weight loss medication now?
Speak to your GP about referral to NHS tier 3 weight management services (access varies by region), or consult a UK-licensed prescriber online to discuss Mounjaro, Wegovy, or Saxenda. Try our free GLP-1 weight loss calculator above to explore potential outcomes with currently available options.
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.