A neuroleptic drug used for treating psychiatric disorders is:

Chlorpromazine is indeed a neuroleptic drug, primarily used in the treatment of psychiatric disorders such as schizophrenia and bipolar disorder. As a first-generation antipsychotic, it works by blocking dopamine receptors in the brain, which helps reduce psychotic symptoms like hallucinations and delusions.

The other options listed serve different purposes: Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID) used to relieve pain and inflammation. Epinephrine is a hormone and medication used in emergencies such as anaphylaxis and cardiac arrest. Streptokinase is an enzyme used to dissolve blood clots in certain conditions, such as myocardial infarction. Each of these drugs plays a crucial role in their respective areas of medicine but does not function as a neuroleptic for treating psychiatric disorders. This context clarifies why chlorpromazine is the best answer for the question regarding neuroleptic drugs.