A rare and potentially deadly brain disorder has been recorded in people taking weight loss drugs, a new study warns.
Wernicke encephalopathy is a neurological condition that causes severe confusion and disorientation, which continue to worsen without treatment.
It is caused by a thiamine, or vitamin B1, deficiency, a nutrient obtained from meats, fish and whole grains that is vital for the functioning of the brain.
In typical cases, not linked to GLP-1s, patients are middle-aged and have an alcohol use disorder, which can interfere with the body’s ability to absorb nutrients, or another condition interfering with nutrient absorption in the intestines.
But now, a study by Israeli researchers says 15 cases of the condition have been diagnosed among people taking GLP-1 drugs.
Eight of the patients were taking semaglutide before they were diagnosed, the active ingredient in Ozempic or Wegovy, and six were on tirzepatide, the active ingredient in Zepbound and Mounjaro. One patient was taking liraglutide, the active ingredient in Saxenda, an older weight loss drug.
They were 59 years old on average and had been taking the drugs for about five months before developing the condition. All reported other symptoms such as gastrointestinal problems.
Dr Dana Lev, an internal medicine expert at Sheba Medical Center and first author of the research, and others wrote in the study: ‘Wernicke encephalopathy is a potentially rare but severe adverse event of [weight loss drug] treatment.
Scientists have warned that weight loss drugs could be linked to Wernicke encephalopathy, a neurological condition that causes severe confusion and disorientation
‘As early detection may prevent [progression], increased clinical awareness is warranted, especially in individuals experiencing severe gastrointestinal symptoms.’
The study only detected an association and does not prove that weight loss drugs cause this potentially deadly brain disorder.
But it is a potential warning signal for clinicians, who are being urged to be aware that patients could develop the condition.
Most of the reported cases came from the FDA’s Adverse Event Reporting System, which is used to report potential side effects from medications.
Reports in this system are unverified because anyone can submit a report. It was set up to act as a crude early warning system for potential drug side effects.
In the study, published in the journal Clinical Nutrition, difficulty walking and confusion were the most common symptoms recorded in patients before diagnosis, with each suffered by seven patients.
Abnormal mental status and paralysis or weakness of the eye muscles were the second most common, each reported in three patients.
Before the patients were diagnosed with the condition, six reported suffering from vomiting, while five suffered from decreased appetite and malnutrition and three suffered from gastroparesis, or paralysis of the stomach.
The condition is caused by a lack of vitamin B1, a vital nutrient for the functioning of the brain
Almost all the cases reported in the study occurred during the reporting year 2023 to 2024. One was recorded during the reporting year 2017 to 2018.
Ten were recorded in the US, while two each were in Europe and Asia and one was reported in South America.
Of the nine patients with prescription information available, four had been prescribed weight loss drugs for their diabetes, three had been prescribed them for weight loss and two had been prescribed them for both weight loss and diabetes.
Eight of the cases were reported by clinicians, while four were reported by healthcare providers and three by consumer attorneys.
It was not clear what may have caused the patients to develop the condition, but the researchers said it could be linked to deficiencies.
They wrote: ‘The prominent weight loss associated with [weight loss drug] treatments alongside the relatively frequent gastrointestinal side effects provides a biologically plausible basis for our findings and suggests increased susceptibility to nutritional deficiencies, including thiamine depletion.’
Although vitamin B1 is vital for the body, it cannot make it itself – instead humans rely on animal and plant sources to ensure a sufficient intake.
Almost everyone gets enough of this vitamin from a standard diet, but weight loss drug users often consume significantly less food than others, putting them at risk of vitamin and mineral deficiencies.
They may also have gastrointestinal problems, which affect nutrient absorption, and vomit regularly, which also reduces the amount of vitamins their body absorbs, raising the risk of deficiencies.
Wernicke encephalopathy has already been linked to patients who undergo bariatric surgery, which can cause malnutrition because a patient cannot eat standard meals for six to eight weeks after the procedure.
Estimates suggest up to 18 percent of bariatric surgery patients develop some degree of vitamin B1 deficiency, raising the risk of suffering from the neurological condition.
Scientists noted, however, that the 15 cases among weight loss drug users were reported out of the millions already taking the medication.
Estimates suggest 30 million Americans have used a weight loss drug at least once to date, equivalent to 11 percent of the population.
Doctors say people with Wernicke encephalopathy have three main symptoms: confusion, inability to coordinate movements and visual changes.
If these symptoms are left untreated, they cause lasting damage to brain and nerve cells, leading to a second condition, Korsakoff syndrome, which causes severe memory loss and the inability to form new memories.
The condition is fatal because it raises the risk of injury and incapacity, which can be life-threatening. It also leaves an individual unable to look after themselves.
Studies suggest up to two percent of people worldwide suffer from Wernicke encephalopathy, although it isn’t clear how many people may have the condition in the US.
Doctors can slowly reverse symptoms of the condition by administering vitamin B1 as pill supplements or injections.
If someone has suffered brain damage already due to the condition, however, they will not be able to completely cure the condition.
Counseling for alcohol use disorder or nutritional support can help to prevent the disease.