How cagrilintide works
Cagrilintide's weight-loss effect begins in a tiny brainstem region called the area postrema, a natural sensor for…
The brainstem switch for fullness
Cagrilintide's weight-loss effect begins in a tiny brainstem region called the area postrema, a natural sensor for appetite hormones in the blood. From there the fullness signal spreads upward into the brain's energy-balance circuitry.
This unit traces that signal from receptor to behavior, shows exactly where it acts in the body, and explains why acting through a distinct circuit is what lets cagrilintide add to GLP-1 rather than merely duplicate it.
Key terms
Where the signal starts
The area postrema is a small region at the caudal end of the fourth ventricle, in the brainstem, with an unusual property: it sits outside the blood-brain barrier, which is what lets it detect substances carried in the blood. That is also why it has long been known as the chemoreceptor trigger zone for vomiting. It is a frontline sensor, and more than 90% of its amylin-responsive cells also respond to glucose.
What makes this circuit compelling is the strength of the evidence. In mice, virally knocking out calcitonin receptors across the caudal hindbrain (the area postrema and the adjacent nucleus tractus solitarius) blunted the food-intake-lowering effect of amylin and of salmon calcitonin. Note the word: blunted, not abolished. That loss-of-function result points the drug's core action at a specific, identifiable brain region rather than a vague systemic effect, but it does not show the region is the whole story, and no source checked here reports the matching gain-of-function experiment.
AdvancedWhy the area postrema is reachable from the blood
Most of the brain is shielded from blood-borne peptides by the blood-brain barrier, so a large circulating peptide like cagrilintide cannot simply diffuse in everywhere. The area postrema is a circumventricular organ, one of the regions a review describes as lacking a blood-brain barrier, and it is uniquely positioned outside that barrier so it can detect blood-borne agents. That anatomy is why a big, albumin-bound peptide can still act centrally: it does not need to cross the barrier, it acts where the barrier is not there.