Reviewed by the Peptica editorial team
Published 5 June 2026
Source-based, neutral information — no medical advice, no sales. Editorial standards
Weight-loss injection has become an umbrella term for a drug class that originally came from diabetes treatment. The best-known members are semaglutide, tirzepatide and, still in testing, retatrutide. They differ mainly in how many signaling pathways they target. This article compares them neutrally based on the evidence, with no dosing, no sources and no medical advice.
What is a weight-loss injection?
Behind the term are so-called incretin mimetics: substances that mimic the body's gut hormones. They influence appetite and blood sugar and are injected weekly. Originally developed for type 2 diabetes, several are now also used for weight management.
One, two or three receptors
- Semaglutide – acts on one receptor (GLP-1). Approved and prescription-only.
- Tirzepatide – acts on two receptors (GIP + GLP-1), often called a twincretin. Approved.
- Retatrutide – acts on three receptors (GIP + GLP-1 + glucagon). Still in clinical testing, not approved.
Put simply: the more pathways engaged, the larger the average effects tended to be in trials.
What trials showed on weight
In head-to-head trials, the tirzepatide group achieved a markedly larger average weight reduction than the semaglutide group. Retatrutide showed even higher average figures in early trials but is not yet approved. Important: actual results depend heavily on individual factors and are often smaller in everyday use than in controlled trials.
Approval status
Semaglutide and tirzepatide are approved, prescription-only medicines in Germany. Retatrutide is still in clinical testing and not regularly available.
Frequently asked questions
Which weight-loss injection works most strongly?+
In trials, tirzepatide showed a larger average weight reduction than semaglutide; retatrutide was higher still in early trials but is not approved. Individual results vary widely.
What's the difference between semaglutide and tirzepatide?+
Semaglutide acts on one receptor (GLP-1), tirzepatide on two (GIP + GLP-1). Both are approved and prescription-only.
Is retatrutide available as a weight-loss injection yet?+
No. Retatrutide is still in clinical testing and not approved.
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