It can, and six published cases prove it happens. A systematic review searched four databases for Wernicke’s encephalopathy after semaglutide prescribed for obesity. It found six [1]. Wernicke’s is what severe thiamine deficiency does to the brain. Thiamine is stored for a matter of weeks. That is short next to how long someone can spend eating very little and vomiting. The broader nutrient picture is in vitamins and minerals on a GLP-1.
A narrative review sets the wider context [2]. Thiamine is one of several micronutrients this drug class is associated with depleting. The route is reduced intake, not impaired absorption. A separate meta-analysis measured what happens to nutritional intake during treatment [3]. Intake is the mechanism. The drug does not consume thiamine. The person stops eating enough of it.
The reason it is worth a reader’s attention anyway is the shape of the sequence, which was the same in every case. Prolonged gastrointestinal symptoms came first. Substantial and rapid weight loss followed. Only then did neurological deterioration appear, presenting as altered mental status and abnormalities of eye movement. The first two stages are visible to the person experiencing them, which makes this a rare harm with an early warning attached.
The outcomes are the reason not to soften any of this. Several cases did badly. One progressed to Korsakoff syndrome, an irreversible amnesic disorder. One ended in death. Wernicke’s is treatable. Treated early with parenteral thiamine, the damage is largely preventable. Left late, it is not.
The practical translation is narrow. Persistent vomiting for weeks is not a side effect to push through. Neither is an inability to keep food down. Rapid weight loss on top of either compounds the problem rather than signaling success. That combination is a reason to contact a prescriber. The dose-escalation period is when it is most likely to arise, as titration and nausea describes.
Nothing here is an argument for taking a supplement on your own initiative. Deficiency severe enough to reach the brain is a clinical emergency. It is treated with injections under supervision. A tablet from a shelf does not address it once symptoms have started. The general problem underneath is eating much less while needing the same nutrients. It sits beside the muscle question in what these drugs do to muscle. The broader tolerability picture is in the network meta-analysis of nineteen drugs.