Which abbreviation represents the action of taking medication by mouth?

The abbreviation that represents the action of taking medication by mouth is SL, which stands for "sublingual." This term specifically refers to the administration of medication under the tongue, where it dissolves and is absorbed into the bloodstream. While SL indicates a method of oral medication administration, it also implies the broader concept of taking substances orally, focusing on a particular technique.

The other options refer to different concepts in medication administration. NPO means "nothing by mouth," indicating that a patient should not receive anything orally, which is the opposite of taking medication by mouth. QID stands for "four times a day," specifying the frequency at which medication should be administered but not indicating the route of administration. PRN means "as needed," referring to when a medication should be given based on a patient's need instead of scheduled times, without clarifying how it should be taken.