Inadequately written prescriptions: prescriber rationales for "take as needed" and "take as directed."

An audit of a large sample of prescriptions written by 39 physicians revealed considerable variation in the rate at which they specified adequate dosage instructions. When asked for their rationales for saying "Take as needed" or "Take as directed" on prescriptions, the physicians cited several circumstances where these instructions may be indicated. "Take as directed;; is defended 1) when the patient has a history of compliance with the regimen being prescribed; 2) when the prescription is accompanied by verbal or auxiliary written instructions; 3) when oral contraceptives are ordered; and 4) when the prescribers may need to make frequent changes in a regimen and wish to communicate these changes orally. "Take as needed" is defended when the drug is to be taken only when the patient determines that sufficient symptoms have appeared. Prescribers are cautioned to consider whether the assumed advantages of nonspecific dosage instructions are outweighed by the possible risks of patient confusion.