Which abbreviation is used for medications that should be taken at night?

The abbreviation HS stands for "hora somni," which translates to "at bedtime" or "hour of sleep." It indicates that the medication should be taken at night, typically before the patient goes to sleep. This is important for medications that may be used to promote sleep or that are intended to work overnight while the patient is resting.

Other options might lead to confusion since they refer to different dosing schedules. PM generally indicates "post meridiem," or the afternoon/evening period, but does not specifically denote when to take the medication. NOC, meaning "nocturnal," can imply nighttime but is not as commonly used to direct the timing of medication as HS. BID refers to "bis in die," or twice daily, which clearly describes a frequency but does not indicate a specific time of day. Hence, HS is the most appropriate abbreviation for medications intended to be taken at night.