A weekly read on the gut, the brain, and the wiring in between. One clinical pearl, one paper, one product, one person. The stuff I actually think about.
1. Practice
Two things to say out loud if you take one of these drugs.
Semaglutide and tirzepatide, sold as Ozempic, Wegovy, Mounjaro, and Zepbound, work by turning down appetite and slowing the stomach. That is the mechanism and it is the whole point. The part that has been slower to arrive: appetite is also how a body gets its vitamins. Turn it down and the vitamins go down with it.
Most of the time that is fine. Bodies carry reserves. But the reserves are not equal. The body stores years of B12 and months of iron. It stores about three weeks of thiamine, vitamin B1.
Thiamine is the vitamin the brain needs to burn sugar. Run out and the brain fails in a specific way: confusion, a walk that goes unsteady, eyes that will not track together. That is Wernicke's encephalopathy. Caught early, it is treated with a few dollars of thiamine. Caught late, the memory damage can be permanent. For a century medicine has taught it as an alcoholic's disease. It is a starvation disease. Alcohol is just the most common way to starve.
First thing to say out loud: the vomiting is the warning.
Nausea is expected on these drugs. Vomiting that goes on for weeks is different. In the case series below, every patient had weeks of gut symptoms and fast weight loss before the brain gave out. The gut trouble is the warning. The brain is the end of the story.
So split it in two.
If you are keeping food down but eating far less and losing weight fast, ask for a thiamine blood level at your next visit, and make sure some thiamine is coming in every day, from food or a multivitamin. A plain multivitamin covers it, which is the Product slot this week.
If you are vomiting most days and your thinking has gone soft, do not reach for a pill. Nothing you swallow is absorbing reliably. That is an emergency department visit. The treatment goes in through a vein. Do not wait for a level. In the hospital we treat on suspicion and let the test confirm us later, because the vitamin is cheap and the miss is permanent.
Four weeks ago I wrote about hospitalized veterans who did not drink. One in four was low on thiamine, and the most common sign was loss of appetite, not confusion (Diseases, 2026). A separate VA clinic checked thiamine in patients with obesity before any surgery. About a third were already low (Obesity, 2025). The people these drugs are prescribed to start the race behind.
Second thing to say out loud: tell the person holding the airway.
The same slowed stomach that keeps you full for hours does not empty on schedule for a procedure. Researchers pooled 13 studies and about 84,000 patients having an upper endoscopy, the camera exam of the stomach. After a standard fast, people on a GLP-1 were about four times as likely to still have food in the stomach, and more of their procedures were called off on the table (Clinical Gastroenterology and Hepatology, 2025). Food in a stomach under sedation can go into the lungs.
The guidance changed in late 2024. Five medical societies, the anesthesiologists among them, now say most people can stay on the drug before a procedure. People who are still climbing the dose, on a high dose, or having nausea, vomiting, or constipation get extra precautions. That can mean a day of clear liquids beforehand, a bedside ultrasound to check the stomach, or a different way of protecting the airway while you are asleep. The older 2023 rule, holding the weekly shot for a week, still shows up on some pre-op instructions.
None of that happens if the anesthesiologist does not know you take it. The scheduler and the surgeon's nurse are not enough. Tell the person holding the airway.
2. Publication
One paper worth reading, in three sentences.
Two researchers, one of them the Korsakoff's specialist in this week's Person slot, searched the medical literature for every published case of Wernicke's in a person taking semaglutide for weight loss, and found six (Bidesie and Oudman, Obesity, 2026). All six had weeks of gut symptoms and heavy weight loss before the neurological collapse, and the outcomes were poor in several, including permanent memory loss and death.
A separate group went through the FDA's side-effect reporting database this year and found 15 cases. Wernicke's was reported a little more than twice as often on these drugs as on other medications, and 7 of the 11 patients with follow-up had lasting neurological damage (Clinical Nutrition, 2026).
Six cases earn the slot because of what they share. Every one of them had a warning phase. Weeks of it. The drug did not cause a sudden collapse. It caused a slow starvation that a blood test could have seen and a few dollars of thiamine could have stopped. The authors' recommendation is the whole issue in one line: when someone on one of these drugs cannot keep food down or is losing weight fast, think thiamine early, and give it through a vein before the brain fails.
Millions of people take these drugs and the overwhelming majority are fine. Nothing here says the drug is dangerous. It says a drug that turns off appetite will run short on the things appetite was delivering. We have known how to prevent this particular shortage since the 1930s.
3. Product
This week's pick: a multivitamin. Unsponsored, no affiliate relationship, no brand.
After weight-loss surgery, a daily multivitamin for life is standard of care. The bariatric surgery society's guidelines say every post-surgery patient should take at least 12 milligrams of thiamine a day, about ten times the daily value (Surgery for Obesity and Related Diseases, 2017). The reasoning is simple. A stomach taking in a fraction of what it used to cannot be trusted to deliver every vitamin. The newer drugs produce surgery-scale drops in intake in some people, and nobody wrote the equivalent rule for the shot.
A review this year pooled six studies and about 480,000 adults on GLP-1s. Vitamin D deficiency rose from about 8 percent at six months to about 14 percent at a year. Iron stores ran roughly a quarter lower than in comparison patients on a different diabetes drug. More than 60 percent of users were eating less calcium and iron than they need, and thiamine and B12 deficits widened the longer people stayed on treatment (Clinical Obesity, 2026). These are observational data and cannot prove the drug did it. They do not need to. Eating less does it.
What to look for: thiamine, B12, iron, vitamin D, and calcium listed at or near 100 percent of the daily value. Skip the “proprietary blends.”
4. Person
One person worth following in this space.
Erik Oudman, a neuropsychologist at Utrecht University who works at the Slingedael Korsakoff Center in Rotterdam, and the senior author of this week's paper.
Korsakoff's syndrome is what Wernicke's becomes when nobody catches it: a permanent inability to form new memories. Oudman spends his working life with the people it happened to. From there he has spent more than a decade taking apart one sentence in every textbook, the one that says this is an alcoholic's disease. He has published systematic reviews of Wernicke's in people who do not drink: after bariatric surgery (2018), in the severe vomiting of pregnancy (2019), in anorexia (2018), in depression (2020), in schizophrenia (2021), in Crohn's disease and colitis (2021), in kidney disease (2024), and in children (2025). Now semaglutide.
Read them in order and a pattern appears. The trigger changes every time. The disease does not. Anyone who stops eating for long enough, for any reason, is on the same clock, and the clock runs about three weeks.
Most of medicine learned this disease on the alcohol ward and filed it there. Oudman documents everyone the filing system missed. His papers are on Google Scholar under his name, and the reviews are plain and free to read.
These drugs work. They lower weight, they lower blood sugar, and the outcome trials show fewer heart attacks. They also change how a person eats. That changes a hundred small things a month, like how the gut behaves and whether the nausea is a bad Tuesday or the third bad week in a row. Almost none of that gets written down. The prescriber sees a weight and a blood pressure every few months. The patient remembers the last few days.
Every case in this week's paper had a warning phase measured in weeks. The information existed. Nobody was holding it in one place.
That is what MeNome is for, our free app at menome.belly-md.com. It does not diagnose anything. It keeps the record, a minute a day, so that when the nausea has been there for three weeks you know it has been three weeks, and so does the person who can do something about it.
We wrote the rule for the surgery and forgot to write it for the shot.
That's the four. See you next week.
Rick
From BellyMD
MeNome is our free app for keeping your own record. A minute a day on your gut, sleep, mood, and energy, and over time it shows you what shows up together. It lives at menome.belly-md.com.
I also make MGB+, a small line of gut-brain supplement formulas: Clear, Cool, and Calm, at belly-md.com. Structure-function support, not a treatment for any disease.
If you want to talk through your own gut-brain picture with me directly, I offer a gut-brain consultation (educational, 500 dollars). Details at belly-md.com.
Not medical advice. This newsletter is for education and does not create a physician-patient relationship. Nothing here is a diagnosis or a prescription. Talk to your own physician before starting, stopping, or combining any medication or supplement, including over-the-counter ones.