Medical Definition of Ad lib

Ad lib: Abbreviation for the Latin "ad libitum" meaning "at pleasure" and "at one's pleasure, as much as one desires, to the full extent of one's wishes." Sometimes seen on a prescription or doctor's order. For example, during an overnight fast when the patient is not to eat any food but can have water, the doctor's order might read: "Water ad lib" (water as desired).

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Last Editorial Review: 5/13/2016

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