WHAT THE TRIALS SHOW
In the studies the FDA reviewed before approving Wegovy, about 1 in 4 people on semaglutide had constipation, compared with about 1 in 10 on placebo. The median symptom duration in the pooled studies was around 47 days. Tirzepatide (Mounjaro and Zepbound) showed a similar pattern: about 1 in 6 people on the peptide had constipation across the dose levels.
THE MECHANISM
The mechanism is straightforward. The peptide slows the gut, total food volume drops, fiber intake usually drops with it, and hydration is often inconsistent. Each of those four shifts makes stool harder and transit slower. Combined, they produce the rate above.
What this means
This one is well-mapped and predictable. The mechanism is settled. Persistent or severe constipation is uncomfortable, can reduce adherence to the peptide, and in rare cases can mask more serious GI issues.
Popular framing treats constipation as a surprise side effect. It is a predictable consequence of slowed transit, and three inputs blunt it.