Does GLP-1 help you feel less hungry?
GLP-1 demonstrably reduces hunger, both as a hormone the body makes naturally and through medicines such as semaglutide. When using those medicines, people lose on average nearly 11% of their body weight.
GLP-1 is a gut hormone your body produces after eating. In studies where the hormone was given directly into the bloodstream, people ate on average around 12% less than they did without it. The higher the dose, the stronger the effect. Higher GLP-1 levels were also linked to a greater sense of fullness and less appetite, although that did not always translate directly into a measurable reduction in food intake. GLP-1 also slows the emptying of the stomach, so you feel full for longer.
Brain-scanning studies show that GLP-1 affects the hunger and fullness centres in the brain differently from the hormone that triggers hunger. These are associations that were measured, not proof of cause and effect.
GLP-1 medicines (such as semaglutide) put this appetite-suppressing effect to practical use for weight loss. People with obesity lost on average nearly 11% of their body weight compared with those taking a dummy pill, and this effect continued for as long as the medicine was used. That said, 17 of the 18 large studies on this were partly funded by the manufacturer. Side effects such as nausea and stomach complaints are common and lead some users to stop taking the medicine. For serious long-term side effects, the certainty of the evidence is low.
For people with binge eating, there are early signs that GLP-1 medicines reduce the number and severity of binge episodes. The evidence is thin, however: the available studies together included fewer than 200 participants. There is no evidence that GLP-1 medicines help with depression or anxiety. An apparently positive signal for fewer thoughts of suicide disappeared entirely in better-designed studies; this safety point is worth noting.
This answer draws on five large summaries of earlier research, including a Cochrane review covering nearly 28,000 participants. The researchers rated the evidence for weight loss and for achieving 5% weight reduction as high certainty. The evidence for side effects leading to stopping the medicine is of moderate certainty, and the effects on serious side effects were rated by the authors themselves as very low certainty. The evidence for binge eating disorder is based on only 182 participants and is therefore thin. The findings about brain mechanisms come from studies measuring associations, not cause and effect.