Constipation is one of the most common complaints on semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound), and it is not a coincidence - these medications deliberately slow gastric emptying and gut motility, which is part of how they curb appetite. Add a sharp drop in food volume (and therefore fiber and fluid), and a backed-up gut is the predictable result. Fiber is the first-line fix, but the type matters more than the brand, and the popular choice is often the wrong one.
A note on framing: this is guidance for managing a common medication side effect with diet, not medical advice. Severe, persistent, or painful constipation, or any alarming symptom, should go to the prescriber managing your medication.
Why the type of fiber matters here
Fibers differ in two ways that decide whether they help or hurt a GLP-1 gut: how much gas they produce when fermented, and how well they hold water. On a slowed, sensitive gut, you want a fiber that eases things through without adding a lot of gas. That single rule reshuffles the usual rankings.
Our top pick: PHGG (Sunfiber)
Partially hydrolyzed guar gum, sold as Sunfiber, is the gentlest well-studied fiber: it is low-FODMAP, produces minimal gas, dissolves clear and tasteless, and has good evidence for improving symptoms and regularity in sensitive guts (Niv 2016). The guar-galactomannan family also has solid metabolic data (Juhasz 2023). For a GLP-1 user, that low-gas profile is exactly the point. See our fiber supplement guide for scored PHGG picks.
Strong second: psyllium
Psyllium is the best-evidenced fiber overall and a reliable, gentle bulk-former that works for constipation without heavy fermentation. It is a great choice if you also want its cholesterol and blood-sugar benefits. The one caution is to take it with plenty of water - it works by gelling, so too little fluid can backfire on an already-slow gut. See our psyllium scorecard.
What to avoid: inulin
Inulin and chicory-root fiber are excellent prebiotics but the most gas-prone fibers there are, because they ferment heavily. On a slowed GLP-1 gut, that is a recipe for bloating and cramping on top of the constipation. Skip inulin (and "prebiotic" gummies built on it) while you are dealing with GLP-1 constipation.
What else helps
- Magnesium. Magnesium citrate draws water into the stool and is a gentle, effective option for GLP-1 constipation specifically - many people find it more reliable than fiber alone for this.
- Fluid. Every fiber needs water to work. Reduced eating usually means reduced drinking, so deliberate hydration is half the fix.
- Movement. Even a daily walk supports motility.
How to take it without making things worse
Start low and build up over one to two weeks - dumping a full dose of fiber onto a slowed gut is the fastest way to trade constipation for cramping. Take it with a full glass of water, drink more through the day, and give it several days to work. If PHGG or psyllium plus water and magnesium is not enough, that is a conversation for your prescriber rather than a reason to megadose fiber.
Bottom line
For Ozempic or Mounjaro constipation, reach for PHGG (Sunfiber) first for its gentle, low-gas profile, or psyllium if you want the broader benefits - and skip inulin, which ferments too much for a slowed gut. Add magnesium citrate and real hydration, and build the dose slowly. Our best fiber supplements guide has the scored picks, and our GLP-1 supplement guide covers the rest of the companion toolkit.