👖 Why does GLP-1 cause constipation?

The last bowel movement was three days ago. On GLP-1, that is not normal.

Constipation is one of the most common side effects on GLP-1 — and the physiology behind it is fairly straightforward. The medication slows gastric emptying, you're eating significantly less food and fiber than before, and reduced fluid intake compounds everything.

GLP-1 receptors are expressed throughout the gastrointestinal tract, not just the stomach. GLP-1 receptor agonists can alter gastrointestinal motility beyond the stomach, which may contribute to constipation alongside lower food and fluid intake. Lower motility plus lower food volume can slow transit overall.

Fiber intake often drops dramatically on GLP-1 without people realizing it — and when fiber drops, bowel regularity often drops with it. Hydration matters more than people think here.

Dehydration concentrates colonic contents and increases 💧 water reabsorption from stool, making it harder and more difficult to pass. On GLP-1, reduced appetite often means reduced fluid intake alongside reduced food intake — both need active attention.