"Take this medicine every day."
Translation:이 약은 매일 복용하세요.
. 은/는 are "tags" used to categorise topic(s) for discussion, similar to the "#" on social media.
. 은/는 can therefore appears in conjunction with other markers (subject; object; location etc.) and even in final verbs.
. As markers do frequently get omitted in a Korean sentence, esp. when their role is clear, this give the wrong impression that they have been replaced by the attached tag 은/는.
So taken as example the above sentence, you can actually have:
이 약은 매일은 복용은 하세요 with 3 separate topics for discussion, namely this medicine; daily; and (?repeat) usage.
The meaning of the sentence is not affected.
In Chinese and Japanese, "복용 (服用)" has the same meaning. When "服" is used as a noun, it means "clothes (양복, 한복,... )", or word used to count medicine (or poison). and when it is used as a verb, it means "take (medicine) by mouth". And there is another meaning of "服 = obey". Was someone ordered to take poison ? hahaha.
은/는 are not subject markers.
They are just tags indicating a theme of discussion. They have no grammatical value besides that.
They can be 'tagged' on to other markers (subject; object; complement...) in a sentence without affecting its meaning.
In sentence construction, the frequent omission of markers does cause misinterpretation of the role of those topic tags.
The example given without omission of markers would look like:
이 약을은 매일 복용하세요
Here, 복용하다 (Take) is a transitive verb conjugated in imperative mode (active voice) and should be translated as such. So, DLG answer is correct.
Your suggestion: This medicine should be taken every day. is in the passive form.
Translated to Korean (without omission of markers), it would probably look like:
이 약이는 매일 복용해야 해요 .