GLP-1 Receptor Agonists

GLP-1 receptor agonists are medicines that reduce hunger by activating receptors for a hormone normally released by the intestine after eating. They mimic glucagon-like peptide-1 (GLP-1) and influence the gut-brain axis, the two-way communication system linking the digestive tract and the brain through hormonal and nerve signals.

The normal gut-brain appetite signal

After a meal, specialised intestinal cells release GLP-1. This hormone helps coordinate the body's response to food, including appetite regulation, stomach emptying and glucose control.

• Intestinal L cells release GLP-1 in response to nutrients entering the gut.
• Gut signals reach appetite-regulating brain circuits through circulating hormones and sensory nerve pathways, including the vagus nerve.
• The brainstem and hypothalamus integrate these signals with information about the body's energy needs, helping determine hunger and fullness.

How receptor agonists reduce food intake

Natural GLP-1 is rapidly broken down. GLP-1 receptor agonists provide more sustained receptor stimulation, strengthening signals that favour eating less. Their effects involve both the brain and the digestive tract, rather than a single pathway.

• Activation of GLP-1 receptors in appetite-regulating neural circuits reduces hunger and increases fullness, making smaller meals more satisfying.
• These medicines can reduce food cravings and the rewarding appeal of food, supporting a reduction in overall energy intake.
• They can slow gastric emptying, so food leaves the stomach more slowly; this contributes to post-meal fullness.
• The relative contribution of nerve signalling, direct brain effects and delayed stomach emptying varies between medicines and with treatment duration; gastric slowing alone does not explain appetite suppression.

What the mechanism means for health care

Weight reduction occurs primarily because people consume less energy, not because these medicines directly burn fat. Their appetite effects accompany glucose-dependent stimulation of insulin secretion, which explains their role in treating type 2 diabetes.

• Appetite suppression is distinct from nausea, although nausea, vomiting and other gastrointestinal adverse effects may occur.
• Medical supervision is necessary because suitability, approved indications, adverse effects and contraindications differ between medicines and patients.
• For obesity care, medication complements nutritional support, physical activity and follow-up rather than replacing comprehensive care.