This article is for educational purposes only. Retatrutide is an investigational medication and is not approved for use in the UK or elsewhere as of July 2026. Tirzepatide and semaglutide are approved medicines in the UK, but this content does not constitute medical advice. Always consult a qualified healthcare professional before starting any weight management treatment. Research peptides are intended for laboratory use only and are not for human consumption.
Introduction
Retatrutide, tirzepatide, and semaglutide are all part of a new generation of medications being studied or used for weight management. While they belong to the same broad category, they work in slightly different ways. This guide compares them based on available clinical data as of 2026.
How They Work
| Medication | Hormone Receptors Targeted | How It Works |
|---|---|---|
| Semaglutide | GLP-1 only | Reduces appetite and slows digestion |
| Tirzepatide | GLP-1 + GIP | Reduces appetite and improves insulin response |
| Retatrutide | GLP-1 + GIP + Glucagon | Reduces appetite, improves insulin response, and may increase energy expenditure |
Retatrutide is unique because it targets three receptors, while tirzepatide targets two and semaglutide targets one.
Weight Loss Results from Studies
Here is a comparison of average weight loss reported in major clinical trials:
| Medication | Average Weight Loss | Study Duration | Status in UK (2026) |
|---|---|---|---|
| Semaglutide | 15–17% | 68–72 weeks | Approved |
| Tirzepatide | 20–26% | 72 weeks | Approved |
| Retatrutide | Up to 28.3% | 80 weeks | Not approved |
Note: These figures come from different clinical trials. Direct comparisons should be made carefully because study designs vary.
Dosing and Administration
All three medications are given as once-weekly injections. Key differences include:
- Semaglutide: Starts low and increases gradually up to 2.4 mg.
- Tirzepatide: Starts low and increases gradually up to 15 mg.
- Retatrutide: In studies, doses up to 12 mg were tested with gradual increases.
Because retatrutide is still investigational, there is no approved dosing schedule available yet.
Side Effects
All three can cause gastrointestinal side effects such as nausea, vomiting, and diarrhoea, especially when doses are increased. Retatrutide may also affect heart rate in some people due to its action on the glucagon receptor. Long-term safety data for retatrutide is still being collected.
Availability in the UK
- Semaglutide and tirzepatide are approved medicines and can be prescribed in the UK (subject to NHS or private availability).
- Retatrutide is not yet approved. It remains in clinical trials.
People interested in currently available treatments should speak with their doctor. Those looking for research compounds should only use suppliers that clearly state products are for laboratory research purposes only.
Those looking for research compounds should only use suppliers that clearly state products are for laboratory research purposes only. You can explore research peptide options on PeptidesX.uk.
Which One Might Be Suitable?
There is no single “best” option for everyone. The right choice depends on individual health conditions, goals, and medical advice. Currently, only semaglutide and tirzepatide are approved options in the UK. Retatrutide may become available in the future if trials continue to show positive results and it receives regulatory approval.
Summary Table
Factor Semaglutide Tirzepatide Retatrutide Receptors Targeted GLP-1 GLP-1 + GIP GLP-1 + GIP + Glucagon Highest Weight Loss ~15-17% ~20-26% Up to 28.3% (in studies) Status in UK Approved Approved Investigational Dosing Once weekly Once weekly Once weekly (studied) Long-term Data Available Available Still being collected
| Factor | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Receptors Targeted | GLP-1 | GLP-1 + GIP | GLP-1 + GIP + Glucagon |
| Highest Weight Loss | ~15-17% | ~20-26% | Up to 28.3% (in studies) |
| Status in UK | Approved | Approved | Investigational |
| Dosing | Once weekly | Once weekly | Once weekly (studied) |
| Long-term Data | Available | Available | Still being collected |
For a complete overview, read our main guide: [Retatrutide for Weight Management: Complete 2026 UK Guide].