The drug most commonly used to treat delirium is haloperidol, which reduces hallucinations and unstructured thought patterns, but also reduces the interaction with the environment. Haloperidol has significant side effects, including extrapyramidal reactions (in 1-10% of patients), neuroleptic malignant syndrome (in which it is the cause in 50% of cases), and prolonged QT syndrome (which can precipitate fatal arrhythmias).