Is there a difference in the medical term hs and qhs?

hs - an abbreviation for the Latin phrase "hora somni", meaning "at bedtime".

qhs - an abbreviation for the Latin phrase "quaque hora somni", meaning "every bedtime".

Therefore, hs would typically be used in a medication prescription to instruct a patient to take a particular medication once at bedtime, whereas qhs would be used to instruct a patient to take a particular medication every night at bedtime.