Not all hallucinations are the result of a neuropsychiatric disorder. Sometimes they result from a vitamin B12 deficiency. And if that's the case, vitamin B12 supplementation can cause the hallucinations to disappear. This is evident from an analysis of fifty case studies by a Dutch psychiatrist, published in Psychopathology in 2024.

Study
Jan Dirk Blom, a psychiatrist specializing in hallucinations, is affiliated with the Parnassia Psychiatric Institute in The Hague. Blom collected fifty previously published case studies of patients in whom doctors had diagnosed both hallucinations and a vitamin B12 deficiency—and had also demonstrated that the deficiency caused the hallucinations.

This was done by administering vitamin B12 to the patients. They usually received injections first to quickly improve their condition, followed by capsules or tablets.

Results
The hallucinations had no distinguishing characteristics from hallucinations not caused by a vitamin B12 deficiency. Patients usually saw or heard things that weren't there.

Click on the figures and table below for a larger version.

In most cases, the hallucinations stemmed from a neuropsychiatric disorder, and the patients also experienced other symptoms, such as paranoia, delusions, or memory problems. In these cases, the patients were prescribed antipsychotics, antidepressants, or other psychotropic medications.

However, in 16 percent of cases, this was not the case. The patients hallucinated but were otherwise mentally healthy.

After starting vitamin B12 supplementation, the hallucinations disappeared within two months in three-quarters of the patients. The remaining quarter showed improvement, but the hallucinations did not disappear completely.

If patients also had other symptoms, these also improved in most cases with vitamin B12 supplementation. This only occurred after the hallucinations had disappeared.

A vitamin B12 deficiency is often accompanied by anemia. Anemia occurred in only 32 percent of cases. This means that most patients did not have the classic symptoms of a vitamin B12 deficiency.

Testing for deficiency
Blom concludes that psychiatrists treating someone with hallucinations should also consider the possibility of a vitamin B12 deficiency. Tests can provide definitive answers.

These tests are especially relevant if the patient belongs to a high-risk group. The table below lists these groups.