Retatrutide.

Activating the GLP-1 receptor to enhance insulin release, slow gastric emptying, and reduce appetite.

Glucagon-like peptide-1 is an incretin hormone released from the gut after a meal. Its receptor is a class B G-protein-coupled receptor found on pancreatic beta cells, on stomach and gut tissue, and on neurons in the hypothalamus and brainstem, including the area postrema. When the receptor is activated, three things happen at once. Beta cells become more responsive to glucose, so insulin secretion rises mainly when blood glucose is already elevated rather than continuously, which is why this class carries a lower intrinsic hypoglycaemia risk than insulin itself. The stomach empties more slowly, flattening the rise in glucose after eating and prolonging the sense of fullness. Central appetite circuits shift toward satiety, reducing the drive to eat between meals. Glucagon secretion is also suppressed when glucose is high. Many compounds target this receptor because native GLP-1 is degraded within minutes by dipeptidyl peptidase-4. Almost every design problem in the class is a half-life problem, and the answers differ. Some analogs attach a fatty-acid chain so the molecule binds albumin and circulates far longer. Others alter the amino acids around the cleavage site so the enzyme cannot act. These structural choices set how often a compound is given and how steeply blood levels rise and fall, which in turn shapes how much nausea a person experiences during the early adjustment period. The class also splits by how many receptors a molecule touches. Pure GLP-1 agonists engage this pathway alone. Dual and triple agonists add GIP, glucagon, or amylin activity on top of it, and combination products pair a GLP-1 agonist with a separate molecule. In every case the GLP-1 arm remains the backbone of the metabolic effect. Of all the pathways described on this site, this one has the strongest and most mature clinical footing. Several GLP-1 receptor agonists are approved medicines for type 2 diabetes, for obesity, or both, and the mechanism has been characterised in humans rather than inferred from animal work. That does not make every molecule in the class equivalent. Some listed here are still investigational, and their receptor activity being well understood says nothing about whether their particular formulation, purity, or long-term profile has been established.

Activating the GIP receptor, a second incretin pathway, usually combined with GLP-1 activity.

Glucose-dependent insulinotropic polypeptide, usually shortened to GIP, is the other major incretin hormone. It is released from K cells in the upper small intestine after eating and acts on a class B G-protein-coupled receptor expressed on pancreatic beta cells, on adipocytes, on bone, and in several brain regions including the hypothalamus. Like GLP-1, it amplifies nutrient-stimulated insulin secretion, so insulin rises in proportion to how much glucose is present. Unlike GLP-1, it does not reliably suppress glucagon and does not slow gastric emptying to the same degree. GIP was studied for decades before it became a drug target, and for much of that time the field was pessimistic. In people with poorly controlled type 2 diabetes the insulin response to GIP appears blunted, which suggested the pathway was a dead end. Interest revived when it became clear that improving glucose control can restore some of that responsiveness, and that GIP receptor activity in fat tissue and in the brain may contribute to weight and appetite regulation through routes that do not overlap with GLP-1. Compounds in this group do not target GIP alone. They are engineered as dual or triple agonists that engage GIP alongside GLP-1, and in some cases glucagon as well, on a single peptide backbone. The design question is not simply whether to include GIP activity but in what ratio, since a molecule can be tuned to favour one receptor over another. Different agents in this space sit at different points on that balance, which is one reason their tolerability and their effect on body weight versus blood glucose are not identical. An unresolved and genuinely debated point is the direction of benefit. Both GIP receptor agonism and GIP receptor blockade have been pursued as approaches to weight management, and the biology that would explain how two opposite interventions could both help is not settled. What is established is that the combined GIP and GLP-1 molecules perform well in human trials and that at least one is an approved medicine. What remains uncertain is how much of that performance is attributable to the GIP arm specifically rather than to the GLP-1 backbone it is attached to.

Engaging the glucagon receptor to raise energy expenditure and mobilise liver fat.

Glucagon is the counter-regulatory partner to insulin, released from pancreatic alpha cells when blood glucose falls. Its receptor is a class B G-protein-coupled receptor concentrated in the liver, with additional expression in kidney, heart, and adipose tissue. Classical glucagon signalling raises blood glucose by driving glycogen breakdown and gluconeogenesis in the liver, which on its face makes it a strange thing to activate deliberately in someone with a metabolic disorder. The rationale rests on glucagon's other actions. Glucagon receptor signalling in the liver also promotes fatty-acid oxidation and reduces hepatic fat accumulation, and across the body it is associated with a rise in resting energy expenditure. In other words it increases the rate at which energy is burned rather than only the rate at which food is refused. Combining that with GLP-1 activity is intended to cancel the unwanted half of the effect: the GLP-1 arm suppresses appetite and improves glucose handling strongly enough to offset the glucose-raising tendency of the glucagon arm, leaving the energy expenditure and liver fat benefits behind. Compounds here take different routes to the same idea. Some are rationally designed multi-agonists built to hit a specific ratio across two or three receptors. Others are derived from oxyntomodulin, a naturally occurring gut hormone that already engages both the GLP-1 and glucagon receptors, and are then modified for stability and duration. The balance between the two arms is the central design variable, and it differs meaningfully between agents. A molecule weighted more heavily toward glucagon may do more for liver fat while demanding more careful attention to glucose. This is a less mature pathway than GLP-1 agonism. No glucagon-receptor-containing agent has the depth of approved-medicine history that pure GLP-1 agonists have, and several of the compounds listed here are still in clinical development rather than in general use. The underlying physiology of glucagon is well established, and the metabolic logic of combining it with an incretin is coherent, but the long-term consequences of chronically raising glucagon signalling in people, including effects on glucose control and cardiovascular parameters over years, are still being worked out. It is also worth noting that the amount of glucagon activity a molecule carries is a design choice made in the laboratory, not something a user can adjust, so comparisons between agents in this class are comparisons between fixed ratios rather than between adjustable ones.

Trial weight-loss signals are very large, among the strongest reported for an injectable.

Magnitude may be comparable at points, but durability and broad metabolic outcomes are still being measured.

Not fully published or independently evaluated yet.

Current adverse-event/discontinuation signals don't support a broad better-tolerated claim.