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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Retatrutide Dosage for Weight Loss
Retatrutide is a prescription-only weight loss injection not yet licensed in the UK, but it represents an emerging option in weight management research. It works as a triple GIP, GLP-1, and glucagon receptor agonist — offering a different mechanism to currently available medications like Mounjaro and Wegovy. This guide explains how retatrutide dosing works, what clinical evidence shows, and how it differs from licensed UK alternatives. Always consult your GP or a qualified healthcare professional before considering any weight loss medication. This information is for educational purposes only.
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Calculate Your BMI Instantly
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 Dosing Works
Retatrutide is administered as a once-weekly injection, similar to Mounjaro (tirzepatide) and Wegovy (semaglutide). The typical dosing schedule involves a gradual escalation over several weeks to minimise side effects and allow the body to adapt.
- Starting dose: 0.5 mg once weekly for weeks 1–4
- Escalation: 1 mg weekly for weeks 5–8
- Further escalation: 1.5 mg weekly for weeks 9–12
- Maintenance doses: 2 mg, 2.5 mg, 3 mg, and up to 4 mg weekly depending on tolerability and response
Each dose increase typically occurs every 4 weeks, allowing time to assess tolerability. The maximum studied dose is 4 mg once weekly. Clinical trials showed retatrutide produced significant weight loss results across all dose levels, with higher doses generally producing greater average weight loss than lower doses. Individual results vary considerably based on lifestyle factors and personal metabolism.
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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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Retatrutide vs Licensed Weight Loss Options in the UK
Unlike Mounjaro and Wegovy — both licensed for NHS and private prescription in the UK — retatrutide is not yet approved by the MHRA for weight management. However, clinical trials (particularly the SURMOUNT trials) have demonstrated that retatrutide may produce greater average weight loss than existing GLP-1 medications.
If you are considering weight management uk options, your GP can discuss licensed alternatives currently available. Using our free GLP-1 weight loss calculator above, you can estimate potential outcomes with approved medications like Mounjaro and Wegovy. Our BMI calculator also helps you understand where your current weight sits within NHS health categories, and our weight converter allows you to track progress across kg, stone, and pounds.
As with all prescription weight loss medications, retatrutide would require a clinical assessment from a licensed prescriber to determine eligibility. Weight loss medications are most effective when combined with reduced-calorie diet and increased physical activity. If retatrutide becomes available in the UK in future, it would likely be prescribed through weight loss medication nhs specialist services or private prescribers, following the same pathways as Mounjaro and Wegovy. Always speak with your GP about the safest and most appropriate option for your individual circumstances.
- 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 licensed for weight loss in the UK?
No. Retatrutide is not yet approved by the MHRA for weight management in the UK. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the currently licensed weight loss injections available in the UK. Retatrutide may become available in future, but this would require MHRA approval first.
How does retatrutide differ from Mounjaro and Wegovy?
Retatrutide is a triple receptor agonist targeting GIP, GLP-1, and glucagon pathways. Mounjaro targets GIP and GLP-1 only. Wegovy targets GLP-1 only. Clinical trials suggest retatrutide may produce greater average weight loss, but it is not yet available for prescription in the UK.
What was the average weight loss in retatrutide clinical trials?
In SURMOUNT trials, retatrutide at the highest dose (4 mg) produced average weight loss of approximately 24% of body weight over 68 weeks. Results varied by dose and individual factors. Clinical trial results do not assures personal outcomes.
Can I get retatrutide through the NHS currently?
No. Retatrutide is not licensed for NHS prescription in the UK. If approved in future, access would likely follow the same pathway as Mounjaro and Wegovy — through specialist weight management services or private prescribing after clinical assessment.
How can I track potential weight loss progress?
Use our free progress tracker above to log your weight across kg, stone, and pounds. Our GLP-1 weight loss calculator helps estimate outcomes with currently licensed medications, and our BMI calculator shows how your weight relates to NHS health categories.
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.