Nausea gets the headlines, but constipation is the GLP-1 side effect people quietly live with for months. It is common, it is in every label, and the advice available online is mostly folklore. What follows separates two things that usually get blurred: how often constipation actually happens on these drugs, which the adverse-reaction tables answer precisely, and what actually relieves constipation, which has been tested in randomized trials — just not in GLP-1 users.
How common it actually is
The Wegovy label reports adverse reactions from its adult weight-management trials against placebo. Among 2,116 adults on semaglutide 2.4 mg once weekly, constipation was reported by 24%, against 11% of the 1,261 on placebo. For context in the same table, nausea was 44% versus 16% and diarrhea 30% versus 16%.[1] So roughly one in four people report it — and the placebo column is a reminder that a meaningful share of that is background rate, not the drug.
| Drug and dose | Constipation reported | Placebo comparator |
|---|---|---|
| Wegovy (semaglutide) 2.4 mg weekly | 24% | 11% |
| Wegovy (semaglutide) 7.2 mg weekly | 20% | 8% (2.4 mg arm: 19%) |
| Zepbound (tirzepatide) 5 mg weekly | 17% | 5% |
| Zepbound (tirzepatide) 10 mg weekly | 14% | 5% |
| Zepbound (tirzepatide) 15 mg weekly | 11% | 5% |
The dose relationship is the surprise
Most GLP-1 side effects behave predictably: they cluster around dose increases and scale with exposure. On the Zepbound label, constipation does the opposite. It was reported by 17% at 5 mg, 14% at 10 mg and 11% at 15 mg — against 5% on placebo — while nausea, diarrhea and vomiting all rose across the same three doses.[2] The semaglutide data point the same way: the label’s higher-dose table puts constipation at 20% on 7.2 mg against 19% on 2.4 mg and 8% on placebo.[1]
These are cross-arm comparisons from label tables, not a controlled test of dose against symptom, so the honest reading is modest: there is no evidence here that pushing the dose up makes constipation worse, which is what most people assume. The practical implication is that constipation is a poor reason on its own to stay at a lower rung of the ladder — a decision better made on the grounds set out in GLP-1 maintenance dosing.
What the evidence supports for relief
Here the sourcing changes. There is no body of randomized trials testing laxatives specifically in people taking GLP-1 medications. What exists is a substantial evidence base in chronic constipation generally, and it is reasonable — but not proven — to expect it to carry over.
A systematic review of 41 randomized trials of at least four weeks’ duration graded the over-the-counter options. Polyethylene glycol–based preparations and senna were supported by good (grade A) evidence and recommended as first-line. Modest (grade B) evidence supported the stimulants bisacodyl and sodium picosulfate, fiber, fruit-based laxatives and magnesium oxide.[3]
Fiber deserves its own note, because it is the intervention people reach for first and get wrong most often. In a meta-analysis of 16 randomized trials with 1,251 participants, 66% of those given fiber responded against 41% of controls (risk ratio 1.48). Two details matter: the benefit was apparent only at doses above roughly 10 g a day, and among specific fibers it was psyllium and pectin that showed significant effects.[4] A spoonful of something fibrous is not the tested intervention.
Why it happens, and why it usually eases
Slowed gastric emptying is not a side effect of these drugs so much as part of how they work — it is a mechanism of the satiety they produce. The same slowing that keeps food in the stomach longer reduces the speed of transit further down. Layered on top is the fact that people eating substantially less are also, by definition, taking in less fiber and often less fluid, which would slow things independently of any drug effect.
That second factor is the one within your control, and it is also the one most likely to be doing the damage. It ties directly to the eating pattern that best supports a GLP-1 — covered in what to eat on a GLP-1 — and to the protein intake that protects lean mass, discussed in GLP-1s and lean-mass loss. For the wider gastrointestinal picture and its timeline, see GLP-1 gastrointestinal side effects and the practical companion, managing GLP-1 nausea, constipation and burping.
The honest bottom line
Constipation on a GLP-1 is common — about one in four on semaglutide 2.4 mg, one in six at the lowest tirzepatide maintenance dose — but it is not a signal that the dose is too high, and the label data give no reason to think it worsens as you titrate up. For relief, the strongest evidence in chronic constipation generally sits with polyethylene glycol and senna, with fiber effective at real doses above about 10 g a day rather than at token ones. None of it has been tested in GLP-1 users specifically, which is worth knowing before anyone sells you a product that claims otherwise.