GLP-1s, Thiamine, and Wernicke’s Encephalopathy

GLP-1s can lower thiamine, leading to rare cases of serious encephalopathy

STUDY: Bidesie J, Oudman E, Obesity 2026

STUDY TYPE: Systematic review of case reports (PRISMA)

FUNDING: Independent

Background

Semaglutide (Ozempic, Wegovy) improves weight loss by suppressing appetite and slowing gastric emptying. Some of its side effects can deplete vitamin B1 (thiamine), like persistent nausea, vomiting, or reduced food intake.

If that goes on too long, thiamine deficiency causes Wernicke’s encephalopathy, a rare, potentially fatal brain disorder classically tied to alcohol use, marked by confusion, abnormal eye movements, and unsteady gait, that can progress to permanent amnesia (Korsakoff syndrome) if untreated.

The Study

• Systematic review (PRISMA, PROSPERO-registered) of PubMed, Embase, CINAHL, and Scopus for published case reports of Wernicke’s encephalopathy following semaglutide treatment for obesity, through February 2026.
• Six unique cases identified: 4 women, 2 men, mean age 47 (range 37–74), treated with semaglutide for a mean of 4.9 months (range 2.5–12) before symptoms began.
• Five of six patients had other chronic conditions, including diabetes, hypertension, thyroid disease, or psychiatric illness.

Results

All six patients had prolonged gastrointestinal symptoms, appetite loss, weakness, vomiting, or constipation, and substantial weight loss before neurological symptoms appeared. Mental status changes (confusion or memory loss) occurred in 5 of 6 cases, abnormal eye movements in 5 of 6, and unsteady gait in 4 of 6; the full classic triad of all three appeared in only half. Of the five patients who got an MRI, all showed the classic Wernicke’s pattern.

Outcomes were often poor: one patient died, four developed permanent memory impairment, and only one fully recovered. Several patients received thiamine doses below the recommended threshold. This is case-report-level evidence, just six patients worldwide, prone to reporting bias, so the true incidence is unknown and likely underestimated, especially since most Wernicke’s cases go undiagnosed even at autopsy.

Practice Implications

1. Ask every patient on semaglutide or another GLP-1 drug about persistent nausea, vomiting, reduced intake, or rapid weight loss at follow-up, especially if they carry other chronic illness. Consider a preventative dose of vitamin B1 (thiamine) 100 mg orally daily.
2. If you suspect Wernicke’s, treat immediately with high-dose IV thiamine (500 mg three times daily). Don’t wait for the labs, as thiamine levels aren’t reliable enough to rule it out and delay worsens outcomes.
3. Tirzepatide and liraglutide are also linked to thiamine deficiency through case reports, so this is likely a class effect.