Definition of q.d. (on prescription)

q.d. (on prescription): Seen on a prescription, q.d. (or qd) means one a day (from the Latin quaque die). The abbreviation is sometimes written without a period in capital letters as 'QD'. However it is written, it is one of a number of hallowed abbreviations of Latin terms that have been traditionally used in prescriptions to specify the frequency with which medicines should be taken.

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Other examples include:

b.i.d. (bid or BID) is twice a day; b.i.d.. stands for 'bis in die' (which means, in Latin, twice a day).
t.i.d. (or tid or TID) is three times a day ; t.i.d. stands for 'ter in die' (in Latin, 3 times a day).
q.i.d. (or qid or QID) is four ti