EP 123:20

GLP-1 side effects: what the trials actually show

Name: GLP-1 side effects: what the trials actually show
Uploaded: 2026-09-28
Duration: 3 min 20 s
Description: Nausea, the slowed stomach, the rare label warnings, muscle loss, the rebound after stopping and the ripple effects on shopping carts: what the trials and regulators actually found.

Nausea, the slowed stomach, the rare label warnings, muscle loss, the rebound after stopping and the ripple effects on shopping carts: what the trials and regulators actually found.

Transcript and sources

Jewelers have reported more people coming in to resize their rings. That's an anecdote, but it points at something real: GLP-1 drugs change more than the number on a scale. So here's what the trials and labels actually say.
The side effect almost everyone hears about is nausea. In the big semaglutide trial, about forty-four in a hundred people felt nauseous. But so did seventeen in a hundred on placebo.
The reason is mechanical. These drugs slow how fast the stomach empties, so food sits there longer. And in animals, a small spot in the brainstem called the area postrema seems to drive the nausea itself.
Most of the nausea came while the dose was being raised, and it usually faded with time. Vomiting and diarrhea matter for another reason: they can dehydrate you, and the labels warn that this can injure the kidneys.
Then there are the rarer warnings. Gallstones were about three times as common as on placebo, but still under two in a hundred people, and fast weight loss itself raises that risk. Pancreatitis is uncommon: about two cases per thousand patient-years.
The boxed thyroid tumour warning comes from rats and mice. Whether it happens in people is still unknown, and the human studies disagree.
In 2025, Europe's regulator concluded that a sudden eye-nerve condition called NAION is a very rare side effect of semaglutide, roughly one extra case per ten thousand years of use. The US labels don't list it, as of this video.
Because food lingers in the stomach, there have been rare reports of stomach contents being inhaled under anesthesia. That's why the labels tell patients to tell their care team before any procedure.
One worry has been cleared. In January 2026, after reviewing ninety-one trials with more than a hundred thousand people, the FDA asked for the suicidal-thoughts warning to be removed.
What about muscle? In a tirzepatide body-scan study, about three quarters of the weight lost was fat and a quarter was lean tissue, the same split seen on placebo. And lean tissue isn't only muscle: it includes water and organs.
Stopping matters too. A year after stopping semaglutide, people in one trial had regained about two thirds of the weight they'd lost.
And the ripples reach past the body. In a Cornell study of about a hundred and fifty thousand households, grocery spending fell about five percent within six months of someone starting a GLP-1, and snacks fell the most. When people stopped, spending went back up.
The most avoidable risk isn't the medicine itself. The FDA has reported people injecting five to twenty times the intended dose of compounded semaglutide, and counterfeit pens with fake needles have been seized.
Most side effects are common, mild and early. The serious ones are rare, and they're on the label. Every source is at peplexicon.com.

Sources