"이 약은 하루에 세번 복용하세요."
Translation:Take this medicine three times a day.
Does anyone say "약을 먹다" any more. Also, why isn't 약 treated as a direct object instead of telling the medicine to take itself?
(약을) 먹다 is a very common expression. The verb (약을) 복용하다 is a very formal one.
So, it is very likely to hear "이 약은 하루 세번 드세요." in a pharmacy.
It might be because of the emphasis being on the 'three times a day'. I thought of it as 'as for this medicine, you take it three times a day'
약 (medicine) is the topic of the sentence, not the subject so "이 약은.." is correct