“Weight-loss injections” have become one of the most discussed topics in metabolic science. Behind the headline phrase sits a family of peptide compounds that act on GLP-1 and related receptors. This guide explains the science: what these compounds are, the mechanisms researchers have studied, and how Ozempic, Mounjaro and Retatrutide differ.
This article is for educational purposes only. It is not medical advice or a recommendation and does not encourage the use of any compound. All products sold by Evil Peptides are for laboratory research use only.
Key points
- The phrase refers mainly to agonists of the GLP-1 receptor, peptides that mimic a gut hormone.
- Semaglutide acts on one receptor, tirzepatide on two and Retatrutide on three.
- Semaglutide and tirzepatide are licensed prescription medicines; Retatrutide remains investigational.
- Reported trial results come from controlled, medically supervised studies.
What are “weight-loss injections”?
The term is used mostly for a group of compounds that imitate hormones produced by the digestive tract, chief among them agonists of the GLP-1 receptor. They were developed and studied in connection with appetite regulation and blood glucose control.
The mechanism in brief
GLP-1 is a hormone involved in satiety, in slowing the rate at which the stomach empties and in regulating blood sugar. Compounds that mimic it have been investigated for their effects on appetite and energy balance. Several newer molecules are designed to act on more than one hormonal pathway at once.
The family: from semaglutide to Retatrutide
| Compound | Receptors targeted | Known brand names | Status |
|---|---|---|---|
| Semaglutide | GLP-1 | Ozempic, Wegovy | Licensed medicine |
| Tirzepatide | GLP-1 + GIP | Mounjaro | Licensed medicine |
| Retatrutide | GLP-1 + GIP + glucagon | None yet | Investigational |
Retatrutide is covered in detail in our full Retatrutide guide.
What about “fat burning”?
The idea of increased energy expenditure is linked mainly to the glucagon pathway, which has been examined in newer compounds such as Retatrutide. This remains an area of active research, and the results reported so far were obtained in controlled clinical trials under medical supervision. They are not evidence of a “magic solution”.
Regulatory status
Semaglutide and tirzepatide are approved as prescription-only medicines in a number of countries, including the UK, where they may only be supplied through a prescriber. Others, such as Retatrutide, are still experimental and have no marketing authorisation. Research-grade compounds are not medicines and are sold for laboratory research only. Any question about weight management should be discussed with a qualified doctor.
Frequently asked questions
What is the difference between Ozempic and Mounjaro?
The number of receptors involved. Ozempic (semaglutide) acts on the GLP-1 receptor alone, while Mounjaro (tirzepatide) acts on both GLP-1 and GIP receptors.
What is the newest compound in this field?
Retatrutide, a triple agonist that is still in clinical research. You can read more in our Retatrutide guide or browse the peptides FAQ.
Research use only: this article is general and educational and is not medical advice. All products sold by Evil Peptides are intended solely for laboratory research and are not for human or veterinary use.