Retatrutide (LY3437943) is a novel GIP/GLP-1/GCG receptor agonist (RA) under investigation for chronic weight management and its complications. It is more potent at the human GIP receptor and less potent at GCG and GLP-1 receptors versus the native hormones, with a half-life of approximately 6 days supporting once-weekly dosing.
Over recent decades, the elucidation of the gut-brain axis and the pivotal role of gastrointestinal hormones in regulating metabolism, appetite, and glucose homeostasis has opened new avenues for pharmacological intervention.
This molecule is more potent at the human GIP receptor (EC50: 0.0643 nM) and less potent at the GLP-1 (EC50: 0.775 nM) and glucagon (EC50: 5.79 nM) receptors. It has a dose-dependent action and causes a decrease in gastric emptying.
GE is a major determinant of glycemic response after food intake. Delayed GE may reduce food intake and subsequently impact weight loss. This controlled delay in gastric emptying is one of the primary mechanisms by which retatrutide promotes satiety and reduces overall caloric intake.
GIP and GLP-1 activity together promote improved glucose regulation, appetite control, and delayed gastric emptying that can enhance metabolic health while combating calorie absorption.
Small Intestine L-cells are responsible for their production from a proglucagon gene. Production of this molecule is also shown to occur in pancreatic α-cells and the central nervous system in areas like the nucleus tractus solitarius and microglia. It predominantly acts by activating a receptor that induces stimulation of insulin release, decreases glucagon secretion, reduces food intake, and delays gastric emptying (GE) by affecting gastric and intestinal motility.
GLP-1 receptor agonists delay gastric emptying, decrease food intake, increase insulin secretion in response to meals, and inhibit glucagon release in hyperglycemic and euglycemic states. GIP also increases insulin secretion after meals and aids in lipid clearance.
Like other incretin-based therapies, Retatrutide’s most frequent side effects are gastrointestinal (GI) in nature. These events are not unexpected, since GLP-1 and GIP receptor activation directly impact appetite, gastric motility, and gut hormone signaling.
Retatrutide’s side effect profile is dose-dependent but manageable, with the majority of issues related to gastrointestinal tolerance. Nausea, vomiting, diarrhea, and abdominal discomfort remain the most common complaints — particularly during the titration phase — but most are mild to moderate and decline once a stable dose is reached.
In clinical trials, most GI symptoms diminished after 8–12 weeks, particularly in participants who followed gradual dose-escalation schedules.
The safety profile of retatrutide was generally favorable, although some adverse events were more common in the treatment groups. Gastrointestinal side effects such as diarrhea, vomiting, and constipation had a higher incidence in the retatrutide groups, particularly at higher doses. Notably, the incidence of nausea was significantly increased across all dose levels. Despite these side effects, the overall incidence of adverse events leading to discontinuation of treatment was relatively low.
Because retatrutide changes how quickly food moves through the gut, some people experience changes in bowel habits. These symptoms are usually temporary and settle as the body adjusts.
The gastrointestinal effects of retatrutide represent a fundamental aspect of its therapeutic mechanism, promoting prolonged satiety, reduced food intake, and improved metabolic outcomes through its interaction with the gut-brain axis.
