Constipation on GLP-1 medications

Where constipation appears in the labels

Constipation is a row in the section 6.1 adverse reaction table of the Ozempic®, Wegovy®, Mounjaro® and Zepbound® labels, and all four Medication Guides list it among the most common side effects. It also sits under the section 5 warning on severe gastrointestinal adverse reactions, which says these reactions are sometimes severe ^{[1][2][3][4][5][6]}.

Section 6.1 of each label notes that rates from different trials cannot be directly compared and may differ from everyday practice. The numbers below describe trial groups; they do not predict your own experience.

Trial rates against placebo

Each figure comes from the US label’s main placebo-controlled pool, and ranges cover the dose groups tested. In the Zepbound® pool the count also includes reports of hard stools.

Other figures in the labels

In the two Wegovy® trials of a higher 7.2 mg dose, constipation was reported by 20% on 7.2 mg, 19% on 2.4 mg and 8% on placebo; in its trial of adolescents, by 6% versus 2% ^[2]. The Mounjaro® label notes that in a cardiovascular outcomes trial of 6,647 adults with type 2 diabetes, constipation was reported by 13% of those on Mounjaro®, one of a handful of reactions it lists as exceptions to an otherwise similar safety picture ^[3].

European and Canadian product information

The European Medicines Agency uses frequency classes: “very common” means at least 1 person in 10 and “common” at least 1 in 100. There is no European Zepbound® listing, because tirzepatide is sold in the EU only as Mounjaro®; the Canadian Zepbound® monograph gives its own trial table instead.

When it starts and how long it lasts

The US labels’ statements about dose escalation name nausea, vomiting and diarrhea, not constipation ^[1][3][5]. The European Wegovy® table is slightly different: it marks constipation, along with the other stomach effects, as mainly seen during the dose-escalation period ^[8].

Where constipation clearly stands apart is duration. In the Wegovy® trials, the median bout of nausea lasted 8 days, diarrhea 3 days and vomiting 2 days, but constipation 47 days ^[8]. A pooled analysis of STEP 1 to 3 likewise reports 24.2% versus 11.1%, with stomach and bowel events on semaglutide mostly mild to moderate ^[11]. Longer does not mean more severe; it does mean a few days of patience may not be enough, and it is reasonable to raise it at your next visit rather than wait it out silently.

Postmarketing reports: the serious end

Section 6.2 of all four US labels lists reactions reported after approval: severe constipation including fecal impaction, ileus and intestinal obstruction, conditions in which the bowel stops moving or becomes blocked. The labels explain that these reports are voluntary and come from a population of uncertain size, so it is not possible to reliably estimate how often they happen or to establish that the medicine caused them ^[1][2][3][5]. The European Ozempic® and Wegovy® tables list intestinal obstruction with a frequency of “not known” for the same reason ^[7][8].

Randomised trials give a different angle. A 2025 meta-analysis of 55 placebo-controlled trials with 106,395 participants found GLP-1 medicines probably have little or no effect on intestinal obstruction, paralytic ileus and several other serious bowel events, while they did raise the risk of gallstones and probably of reflux ^[12]. Trials may miss rare events, and the labels’ listing remains a reason not to brush off constipation that is severe or lasting.

Why it may happen

What the labels support: the labels do not explain why constipation happens. They do report reduced food intake: the Mounjaro® label lists decreased appetite as a common reaction, and the European Wegovy® information says semaglutide reduces energy intake and hunger ^[3][8].

What is proposed but not measured: it is plausible that eating and drinking less, combined with the medicines’ effects on the gut, slows the bowel. None of the labels states this as the cause.

General medical background: the NIH lists not eating enough fibre, not drinking enough liquids, changing how much and what you eat, and changing your medicines among the everyday causes of constipation ^[13]. Several of these can change at the start of a GLP-1 medicine, which is why it is worth noting your food and drink alongside your doses.

What else could it be

Constipation is common for reasons unrelated to GLP-1 medicines. The NIH lists medicines and supplements that can make it worse, including antacids containing aluminium or calcium, iron supplements, opioid pain medicines, some antidepressants, diuretics, calcium channel blockers and anticonvulsants ^[13]. It also names routine changes such as travel, pregnancy and ageing, and conditions such as diabetes itself, an underactive thyroid, irritable bowel syndrome and coeliac disease ^[13].

If you started another medicine or supplement around the same time, mention it: the constipation may have more than one cause.

What general guidance suggests

The Medication Guides give no specific advice for constipation: they do not mention fibre, laxatives or particular foods. Their advice to drink fluids appears in the dehydration warning, which is about fluid lost through diarrhea, nausea and vomiting ^[2][4][6]. General guidance from the NIH fills part of that gap; it is written for constipation in general, not for GLP-1 medicines.

• Add fibre a little at a time so your body can adjust, and drink water and other liquids so the fibre works better. Whole grains, beans and lentils, fruit, vegetables and nuts are the examples it gives ^[15].
• How much to drink depends on your size, health, activity and climate, so the NIH suggests asking a health professional rather than giving one figure ^[15].
• Regular physical activity, giving yourself enough time and going as soon as you feel the urge may help ^[14].
• Laxatives are something your health care professional may suggest for a short time and choose the type of. Do not stop or change a prescribed medicine on your own ^[14].

What to write down

Constipation is easiest to describe with simple counts: the date of each bowel movement, how many days passed between them, whether stools were hard or painful to pass, and any bloating or stomach pain. Add how much you drank, what you ate and how many days after your injection the change began. Note a recent dose increase, and anything you took for it.

Over a few weeks this shows whether constipation is steady, getting worse or easing, which tells your clinician far more than a general impression.

Ozempic® and Wegovy® are registered trademarks of Novo Nordisk A/S. Mounjaro® and Zepbound® are registered trademarks of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Novo Nordisk or Eli Lilly and Company.

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