"I'm a few weeks in, I feel great, I'm eating way less, and I haven't had a real bowel movement in four days. Is that normal?" We hear some version of that at check-ins all the time, usually asked quietly and a little apologetically. It is common enough that it showed up in roughly one of every four people taking semaglutide in the big weight-loss trials, so you're far from the only one wondering.
Constipation tends to get less attention than nausea, even though it is one of the most commonly reported digestive side effects on these medications.
The Quick Answer
Constipation is a common side effect of GLP-1 medications. In the weight-management trials behind the semaglutide 2.4 mg label, 24% of people on the drug reported constipation versus 11% on placebo.1 In the SURMOUNT-1 tirzepatide trial it was reported by 12% to 17% of people depending on dose, versus 6% on placebo.2 These medications delay gastric emptying and slow gut motility, and a recent clinician review suggests lifestyle changes first, then polyethylene glycol (PEG 3350) as a first-line medication if needed.13 Severe or painful constipation, vomiting, or a swollen belly needs a call to your provider.
How Common GLP-1 Constipation Is
The cleanest numbers come from the prescribing information and the pivotal trials, where every participant was asked the same questions on the same schedule. Placebo groups matter here, because plenty of people in a weight-loss study eat differently and move less than usual, and some of them get constipated with no drug involved.
| Medication and source | Constipation on drug | Constipation on placebo |
|---|---|---|
| Semaglutide 2.4 mg, weight-management trials (prescribing information) | 24% | 11% |
| Tirzepatide 5 mg, SURMOUNT-1 | 17% | 6% |
| Tirzepatide 10 mg, SURMOUNT-1 | 17% | 6% |
| Tirzepatide 15 mg, SURMOUNT-1 | 12% | 6% |
A 2024 JAMA review of obesity medications put the range for constipation at 11% to 24% across the drugs it covered.4 A 2026 clinician-education piece in American Family Physician cites endocrinologists who see it in 10% to 20% of their patients, with higher rates in people who were already prone to constipation.3
Tirzepatide at the highest dose had the lowest rate of the three tirzepatide groups. Nobody has a tidy explanation for that, and these were separate trials with different populations, so the table is a way to see how common the problem is and not a way to rank the two medications against each other.
Why It Happens
Both medications slow the stomach's emptying. The semaglutide label states plainly that the drug "delays gastric emptying," and slower movement through the upper digestive tract is part of why you feel full sooner and stay full longer.1 The same effect on gut motility is the main mechanism clinicians point to for constipation, along with a link to how fast the weight comes off.3
Then there's the ordinary arithmetic of eating less. Stool is made largely of fiber and water. If your appetite drops by a third, the amount of bulk reaching your colon drops with it, and plenty of people also drink less than before because thirst and hunger signals both get quieter. Those two factors aren't measured in the trials above, so treat them as the explanation clinicians commonly give and not as something the data has pinned down.
Some medications make it worse. The American Family Physician review lists anticholinergics, opioids, and ondansetron as drugs that also affect gut motility, and it flags a history of gastroparesis as a reason for extra caution.3 If you take any of those, mention it at your consultation.
When It Tends to Show Up
Gastrointestinal side effects cluster around the early weeks and each dose increase. For nausea, vomiting, and diarrhea, tirzepatide's trial data says most events happened during dose escalation and became less frequent over time.2 The sources I could verify don't make that same claim for constipation specifically, so it's reasonable to expect it may ease as your body adjusts, but it's also possible for it to hang around for as long as your eating and fluid habits stay changed.
Your own history matters too. The AFP review reports that gastroenterologists see worsening in roughly half of patients who already had advanced constipation before they started.3 If you've dealt with it for years, it's worth saying so before your first injection so the plan is ready.
What May Help
There's no large trial testing one fix against another in people on GLP-1s, so what follows reflects clinician guidance and general constipation care. Your provider should shape it around your history.
Water, first. Aim to drink on a schedule instead of waiting for thirst, since the medication tends to dull it. This is also the habit that protects your kidneys when nausea or diarrhea shows up, which we cover in our post on GLP-1s and kidney health.
Walking. The AFP review includes daily walking and general mobility among its first-line suggestions.3 A 10 to 15 minute walk after meals is an easy place to start, and it has the side benefit of supporting the muscle you're trying to hold onto.
Fiber, added slowly. When you're eating less food overall, vegetables, fruit, beans, and whole grains are where fiber comes from, and protein-first eating can crowd them out. Adding fiber gradually matters because a sudden jump, especially without enough water, can bloat you and make a sluggish gut feel worse. Our guide on what to eat on a GLP-1 covers how to get protein and fiber onto the same plate.
An osmotic laxative, if lifestyle isn't enough. The AFP review recommends polyethylene glycol (PEG 3350) as the first-line medication, with stimulant laxatives such as senna or bisacodyl as a second step.3 A gastroenterologist quoted in the American College of Gastroenterology's guidance describes treating with an osmotic laxative "without lowering the dose" of the GLP-1.5 Ask your provider which option fits you and how long to use it before you start one.
What to Avoid Doing on Your Own
Two habits cause trouble. The first is skipping or changing your own dose to get relief. Dose changes belong to your prescriber, and an unplanned gap or a lower dose can affect how well the rest of your plan works. The second is stacking laxatives for several days when nothing happens. If simple measures haven't worked within a few days, that's the point to message your care team instead of escalating at home.
When to Call Us
Most constipation on these medications is uncomfortable and not dangerous. A small number of cases aren't. The semaglutide label lists ileus, intestinal obstruction, and severe constipation including fecal impaction among serious reactions reported after approval.1 Call your provider the same day, or seek urgent care, if you have any of the following:
- Severe or worsening belly pain
- Repeated vomiting, or you can't keep fluids down
- A swollen, hard abdomen, or you can't pass gas
- Blood in your stool
- No bowel movement for several days despite the steps above
These can also overlap with other conditions, such as gallbladder problems, so don't try to diagnose yourself from a list.
How We Handle It at Defiant
Our GLP-1 programs, which start at $295 a month, include weekly nurse check-ins and bi-weekly titration check-ins at our Lisle clinic, so constipation tends to get raised early instead of after a week of suffering through it. Your provider reviews your history and current medications at your consultation, and they decide whether a dose pace, a hydration and fiber plan, or a laxative makes sense for you. If you're in Naperville, Downers Grove, Oak Brook, or Wheaton, that's a short drive, and the weekly nurse check-ins keep it on the radar between visits.
If you're comparing programs, our overview of medical weight loss at Defiant lays out what's included.
- Constipation was reported by 24% of people on semaglutide 2.4 mg versus 11% on placebo, and by 12% to 17% on tirzepatide versus 6% on placebo.
- GLP-1 medications delay gastric emptying and slow gut motility, and eating and drinking less may add to it.
- Clinician guidance generally starts with fluids, walking, and gradual fiber, then moves to polyethylene glycol if needed, under a provider's direction.
- Don't change your GLP-1 dose on your own to fix constipation.
- Severe pain, repeated vomiting, a swollen belly, or blood in the stool needs a same-day call.
Frequently Asked Questions
A Few Weeks In and Something Feels Off?
If you're thinking about starting a GLP-1, or you're a few weeks in and the digestive side is getting to you, bring it to a visit. Our Lisle team runs weekly nurse check-ins and bi-weekly titration so side effects get handled early.
Last updated October 7, 2026.
References
- Semaglutide 2.4 mg prescribing information (adverse reactions; delayed gastric emptying; postmarketing ileus, intestinal obstruction, and severe constipation including fecal impaction). DailyMed
- Eli Lilly Medical Information. Gastrointestinal adverse events reported in tirzepatide clinical studies (SURMOUNT-1): constipation 17%, 17%, and 12% at 5, 10, and 15 mg versus 6% on placebo. Lilly Medical
- Vega CP, Montanero G, Jacob L. Managing constipation associated with GLP-1 receptor agonist therapy. American Family Physician. August 2026. AAFP
- Gudzune KA, Kushner RF. Medications for Obesity: A Review. JAMA. 2024;332(7):571-584. PubMed
- American College of Gastroenterology. GI adverse events with GLP-1 receptor agonists for weight loss: understanding the risks. 2023. ACG