GLP-1 medications slow down your entire digestive tract, starting in the stomach. That slowing is part of how they keep you full, but it changes how your whole gut feels and works.

In the stomach: delayed emptying
Normally, the stomach empties a meal into the small intestine over a few hours. GLP-1s relax the stomach and tighten the valve at its exit (the pylorus), so food can stay in the stomach for much longer than usual, sometimes many hours after eating. This is why so many people on GLP-1s experience:

• Nausea, especially after larger or fattier meals
• Feeling full after just a few bites, and staying full for hours
• Reflux and heartburn, as a full stomach pushes contents upward
• Burping, including sulfur-smelling burps from food sitting and fermenting in the stomach
• Vomiting, sometimes of food eaten many hours earlier

In the intestines and colon: slower transit
The slowing continues through the intestines, which affects your bowels:

• Harder stool: the longer stool sits in the colon, the more water is absorbed from it, so it becomes harder, drier and more difficult to pass.
• Less food, less bulk: smaller portions mean less fibre and volume to stimulate the bowel.
• Less fluid: appetite and thirst often drop together, and even mild dehydration makes stool harder.
• Trapped gas: when stool moves slowly, gas gets trapped behind it, causing pressure and bloating.
• Weaker bowel signals: with less food coming in, the natural reflex that stimulates the colon after meals is weaker, so the urge to go comes less often.

Symptoms are often strongest in the first few weeks after starting or increasing a dose. A healthy bowel empties one to three times a day, and on a GLP-1, many people find they go far less often.