GLP-1 Drug Exenatide Separates Eating From Pleasure and Anticipation in Primates

Five adult male rhesus macaques were tested using a novel operant food intake paradigm with four meal schedule conditions. Two pellet types with different palatability values were offered in all combinations across two consecutive daily feeding sessions. Exenatide (1 μg/kg) was administered subcutaneously 1 hour before the first session. Food intake, pellet preferences, and blood glucose were measured across conditions.

One of the biggest concerns about GLP-1 weight loss drugs is whether they work by making food less pleasurable — which could contribute to depression or anhedonia in some patients. This study provides nuanced evidence that GLP-1 agonists primarily suppress the drive to eat while initially preserving hedonic experience, with pleasure-dampening effects appearing later and more weakly. Understanding this distinction is crucial for predicting psychological side effects.

As millions of people take GLP-1 agonists for weight loss, understanding exactly how these drugs change the brain's relationship with food is increasingly important. Reports of reduced interest in food, alcohol, and other pleasures have raised questions about whether GLP-1 drugs affect the reward system broadly. This primate study provides some of the most detailed behavioral evidence to date, showing the effects are more nuanced than simple appetite suppression.

The study used only 5 male rhesus macaques, which is a very small sample size even for primate research. Only a single acute dose was tested — chronic dosing may produce different effects on hedonic regulation. The translation from macaque food preference behavior to human subjective experience of food pleasure is uncertain. Blood glucose changes (hypoglycemia) may have independently influenced feeding behavior.