"Θα έχουν φέρει το φάρμακο μέχρι αύριο."

[Lyazko]

I tried "they will have brought the drug by tomorrow", and was told that drug≠medicine, but here in the US drug=medicine. The terms are virtually coextensive. It would be exceptional for someone to be unable to use the terms interchangeably.

[I.Schmidt1]

my translation was >they will have brought the medicine until tomorrow<
until was marked wrong - why?

[mizinamo]

Because the perfect tense refers to the completion of an action, not to a duration.

A completion does not take a long time, but "until" refers to an action that lasts a long time (and ends at a specific time).

"by tomorrow" means that the action takes place somewhere between now and tomorrow, but "until tomorrow" means that the action takes place all the time (continuously) from now and ending tomorrow.

[I.Schmidt1]

thank you, got it