The Therapeutic Interchange Program (TIP) has developed a process allowing physicians and other prescribers to endorse the Washington State Preferred Drug List (PDL), and requires pharmacists to automatically substitute the preferred drug for non preferred drugs prescribed by these practitioners unless the prescription is for a refill of an antipsychotic, antidepressant, chemotherapy, antiretroviral, or immunosuppressive drug, in which case the pharmacist shall dispense the prescribed non preferred drug.
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