What adverse effect can occur with haloperidol treatment?

Haloperidol is an antipsychotic medication commonly used to treat psychotic disorders, such as schizophrenia, and it belongs to the class of drugs known as typical antipsychotics. One of the well-documented adverse effects associated with haloperidol treatment is the occurrence of extrapyramidal symptoms (EPS). These symptoms may include tremors, rigidity, bradykinesia, and tardive dyskinesia, which are movement-related disorders that arise due to the drug's effect on the dopamine pathways in the brain, particularly within the extrapyramidal system.

Haloperidol works primarily by blocking dopamine D2 receptors, which is effective for controlling positive symptoms of psychosis but also leads to these adverse motor side effects. The risk of developing EPS is a significant concern and is a fundamental reason for monitoring patients on this medication closely. In contrast, while weight gain and increased sleepiness can occur with some antipsychotics, they are more commonly associated with atypical antipsychotics rather than typical ones like haloperidol. Vision changes are not a well-recognized adverse effect of haloperidol, making extrapyramidal symptoms the correct answer in this context.