GLP-1s and SIBO

Is there a connection?

GLP-1 medications keep coming up. They are everywhere right now, and they come up most often around the weight that shows up after menopause, when estrogen drops and the body quietly rewrites the rules about where it stores fat. Habits that worked for decades stop working. It is a real problem and these drugs do produce real weight loss.

That is the part everybody already knows. What sent me looking was a different thought, and it started with something we talk about here constantly.

SIBO.

Picture the gut as a conveyor belt. Food moves along it at a certain pace, and that pace is doing real work. When the belt slows, contents sit longer than they should, and bacteria that belong further down the line start growing where they do not belong. Small intestinal bacterial overgrowth. Slowed motility sits at the center of it, which is why it turns up alongside opioid use, diabetic gastroparesis, and a handful of other conditions that share nothing except a gut that has stopped moving at normal speed.

So here is the thought. GLP-1 medications work in part by slowing gastric emptying and peristalsis. That is not an unwanted side effect. That is the mechanism. Food stays in the stomach longer, so appetite drops and fullness lasts. Which means these drugs deliberately create the exact condition that overgrowth needs.

I did not know whether anyone had looked at that. It turns out some people have. Early observational work is beginning to examine SIBO rates in people who go on these medications, and the honest summary is that the signal is there and the size of it is not settled. The mechanism, though, is not speculative at all. Slower movement means more stasis, and more stasis means more room for bacteria to set up where they should not be.

For a community that discusses SIBO as much as ours does, that is not a footnote.

And there is a second question underneath the first one, which nobody seems to have asked at all. Whether these medications make things worse for someone who already has SIBO has not been studied. To be clear, I am not saying they do. I am saying nobody knows, and meanwhile existing SIBO or a long history of bloating and distention rarely factors into the decision to prescribe one. These drugs get prescribed on weight and metabolic numbers. Gut history usually never comes up. It should.

The wider gut picture is filling in as these medications accumulate years of real world use. Nausea, constipation, regurgitation, delayed gastric emptying, and in more serious cases gastroparesis and bowel obstruction have been reported, and litigation has followed around severe gastrointestinal injury. None of that means these drugs do not work. It means time is the only thing that shows what a medication actually does out in the world, long after the marketing has moved on.

William Osler is supposed to have said that doctors should use new remedies quickly while they still work. People read that as enthusiasm. It reads to me as a warning. In my years of practice, I used new medications judiciously rather than jumping on the bandwagon.

This is what pattern recognition looks like in practice. Two things sitting in plain sight, a drug class built on slowing the gut and a condition caused by a slow gut, and the connection between them still getting worked out. Worth knowing before starting one, and worth knowing for anyone already on one who has noticed something new in the gut.

Stay curious and thrive,

Dr. G

Authored by Gerard Guillory, MD

Gerard Guillory, MD, is a board-certified internist who practiced for nearly four decades with a focus on functional, root-cause medicine. He is the author of three books on irritable bowel syndrome and the founder of It’s My Health, where he and his team put current health news in context and help members understand the underlying causes of chronic symptoms.