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. Zepbound's label reports constipation at 17%, 14%, and 11% across the 5, 10, and 15 mg doses, versus 5% with placebo.
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
References4 sources
How to read these sources
This article uses primary sources and reviews to separate mechanism, human evidence, and context.
- Human Trial
Massachusetts Medical SocietyOnce-Weekly Semaglutide in Adults with Overweight or Obesity Read source
Used Here ForGrounding the constipation question in the STEP 1 trial's gastrointestinal adverse-event data.
Good ForTrial-measured frequency of gastrointestinal side effects with semaglutide 2.4 mg.
Not ForPredicting a specific person's GI symptoms or severity.
New England Journal of Medicine 384(11):989-1002 - Official Label
FDA-approved prescribing information (Wegovy)
U.S. Food and Drug Administration / Novo NordiskWEGOVY (semaglutide) prescribing information: 6 Adverse Reactions Read source
Used Here ForChecking the constipation rates the approved label reports.
Good ForThe FDA-approved adverse-reaction rates from the weight-management trials.
Not ForPredicting a specific person's GI symptoms.
FDA-approved labeling, DailyMed (National Library of Medicine), updated June 18, 2026 - Human Trial
Diabetes, Obesity and Metabolism
WileyGastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss Read source
Used Here ForAdding the pooled STEP 1 to 3 analysis of how often gastrointestinal events occurred and how long they lasted.
Good ForPooled trial data on the gastrointestinal tolerability of semaglutide 2.4 mg.
Not ForPredicting a specific person's GI symptoms.
Diabetes, Obesity and Metabolism 24(1):94-105 - Human TrialMassachusetts Medical Society
Tirzepatide Once Weekly for the Treatment of Obesity Read source
Used Here ForAdding the tirzepatide gastrointestinal adverse-event rates from SURMOUNT-1.
Good ForTrial-measured gastrointestinal side effects of tirzepatide across doses.
Not ForPredicting a specific person's GI symptoms.
New England Journal of Medicine 387(3):205-216