Potential danger to use two antipsychotic medications together

*(This will be used for comment to a student ordering 2 antipsychotic medications together for an schizophrenic patient)*

Haldol and Zyprexa are antipsychotic medications. Why can it be dangerous to use two antipsychotic medications together? (the answer can be related to the use of medications on the same classification potentiate side effects and concentration in the blood).

Comment and explain using any citation relate to it: *My preceptor likes to use Congentin with  antipsychotics medications (like ordering Haldol plus congentin) to prevent extrapyramidal or involuntary muscle movements caused by antipsychotic medications. That helps the patient continue using the medication since it prevents side effects.

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