Constipation on GLP-1 medications: what helps and when to get care
How often constipation showed up in semaglutide and tirzepatide trials, the food and over-the-counter steps four medical societies suggest, and the symptoms that shouldn't wait.
Do GLP-1 medications cause constipation?
Constipation is a common side effect of GLP-1 medications. In obesity trials it was reported by 24% of people on semaglutide 2.4 mg versus 11% on placebo, and by 11% on tirzepatide 15 mg versus 5% on placebo. A 2025 joint advisory notes constipation is common with weight loss and that digestive side effects are most likely when starting or raising the dose [1].
Key numbers
- In obesity trials, constipation was reported by 24% of people on semaglutide 2.4 mg versus 11% on placebo, and by 11% on tirzepatide 15 mg versus 5% [1].
- Digestive side effects are most likely in the first weeks and after dose increases, and tend to ease on a stable dose [1].
- A 2025 joint advisory suggests fluids and gradually more fiber from food first, then options such as magnesium, fiber supplements, polyethylene glycol 3350 or stool softeners [1].
- The NIH upper limit for magnesium from supplements and medicines is 350 mg a day for adults, and toxicity risk is higher with impaired kidney function [2].
How long does constipation last on a GLP-1?
Digestive side effects from GLP-1 medications tend to ease on a stable dose. The 2025 advisory says they are more likely in the first weeks of treatment and after dose increases, and that they tend to decrease in frequency and severity with continued use. It gives no specific timeline for constipation itself [1].
In the clinical trials, participants were allowed to stay at a dose for up to 8 weeks to let digestive side effects settle before moving up, and fewer than 10% stopped treatment because of digestive problems [1]. How quickly to raise your dose is your prescriber's decision.
What helps constipation on a GLP-1?
Fluids and fiber-rich foods are the first step for constipation on a GLP-1. The 2025 advisory recommends adequate fluids, gradually adding fiber from foods such as prunes or other dried fruit, and water-rich fruits and vegetables. If food changes aren't enough, it lists daily magnesium, fiber supplements, polyethylene glycol 3350 and stool softeners as options [1].
- Drink enough fluids through the day [1].
- Add fiber-rich foods gradually, such as prunes or other dried fruit [1].
- Favor water-rich fruits and vegetables [1].
- If high-fat or very high-protein meals seem to make constipation worse, the advisory says limiting them for a short time may help [1].
- If food changes aren't enough: daily magnesium adjusted to keep bowel movements regular, fiber supplements, polyethylene glycol 3350 or stool softeners [1].
Don't cut protein for long: low protein intake from reduced appetite may contribute to muscle loss on these medications [1]. See our guide to protein on a GLP-1 medication.
Constipation that drags on can also lead to reactive diarrhea. If you take anti-nausea medicine, the advisory notes ondansetron can worsen constipation and that prochlorperazine may be preferable; which one to use is your prescriber's call [1].
Is magnesium citrate safe for constipation on a GLP-1?
Magnesium citrate is one option the 2025 advisory describes as effective and well tolerated for constipation on a GLP-1, with the daily amount adjusted to keep bowel movements regular [1]. The NIH sets the adult upper limit for magnesium from supplements and medicines at 350 mg a day, and says toxicity risk rises with impaired kidney function [2]. Check with your prescriber first if you have kidney disease.
Magnesium adds up across products. High intakes from supplements and medicines can cause diarrhea, nausea and cramping, and magnesium is also in some laxatives and heartburn products [3]. Protocol One contains 200 mg of magnesium [4], so anyone taking it who adds magnesium for constipation should count every source against the 350 mg limit [2].
When constipation needs urgent care
Get medical care promptly if constipation comes with any of these:
- Severe or worsening belly pain
- A swollen, hard belly
- Vomiting, especially if you can't keep fluids down
- Being unable to pass gas or stool
In September 2023 the FDA added ileus, a blockage of the intestine, to Ozempic's labeling after postmarketing reports; the Wegovy and Mounjaro labels already listed it [5, 6]. Because those reports are voluntary, the labels say it isn't possible to reliably estimate how often it happens or to establish that the drug caused it [6].
Dehydration from severe vomiting or diarrhea can cause acute kidney injury, the 2025 advisory warns, so don't wait it out if you can't keep fluids down [1].
Where Understory fits
Understory Nutrition sells Protocol One, a daily supplement designed to be taken alongside a GLP-1 medication. It is not a constipation treatment, and we make no constipation claim for its magnesium or its digestive comfort blend. The magnesium it contains counts toward the upper limit described above.
What this evidence can't tell you
- The constipation rates come from obesity trials with follow-up of up to 68 weeks for semaglutide and 72 weeks for tirzepatide; rates in everyday use may differ [1].
- The relief steps are expert recommendations drawn from the literature and clinical experience, not trials testing each step in people on GLP-1 medications [1].
- The ileus label change is based on voluntary reports and doesn't show how often it happens [6].
Sources
- Mozaffarian D, Agarwal M, Aggarwal M, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. Obesity. 2025;33(8):1475-1503. doi:10.1002/oby.24336 Full text. Expert advisory published in four journals; this page cites the Obesity version.
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. ods.od.nih.gov.
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Consumers. ods.od.nih.gov.
- Understory Nutrition. Daily Micronutrient & Digestive Protocol, Supplement Facts label. Product page.
- Healio. FDA updates Ozempic label to include warning for intestinal blockage, hypoglycemia risk. September 29, 2023. healio.com. News report of an FDA safety labeling change.
- CBS News. FDA updates Ozempic label with potential blocked intestines side effect, also reported with Wegovy and Mounjaro. September 28, 2023. cbsnews.com. News report quoting the label's voluntary-report statement.
These statements have not been evaluated by the Food and Drug Administration. Understory Nutrition products are not intended to diagnose, treat, cure, or prevent any disease. This page is general information, not medical advice. Talk with your prescriber or pharmacist before starting a laxative or supplement, especially if you have kidney disease.