Thiamine - vitamin B1 - can potentially cause a fatal brain disorder called Wernicke encephalopathy.
Wernicke encephalopathy typically occurs in people who have disorders such as alcoholism and anorexia that lead to malnourishment and is an example of the wide range of brain diseases called encephalopathies that are caused by metabolic disorders and toxic substances
Symptoms can include confusion, hallucinations, coma, loss of muscle coordination and vision problems such as double vision and involuntary eye movements. Untreated, the condition can lead to irreversible brain damage and death.
Acute encephalopathy has a rapid onset of between hours and days. It is commonly due to toxic and metabolic factors.