I was going through a sentence mining deck I’d neglected/procrastinated for too long and came across this sentence; I probably yanked it from an NHK news article. There is a phrase within the sentence which I understand from a “feel the language (like one ‘feels’ jazz music)” kind of way, but I am uncertain that I understand it logically:
A medicine that’s drunk by means of the mouth – it seems like から is behaving like で in here? Basic Grammar Dictionary does not mention this usage of から。
My best guess is: is it because the medicine itself has a direction when one is in the process of drinking it? In that, beginning its journey, it starts FROM the mouth and, implicitly, TO the rest of the body?
Likewise, would 「口で飲む薬」 not also have been just as equally valid grammar?
As well as what’s already been said I’d note that this phrasing seems to be used specifically with medicine. English also has a specific bit of phrasing that gets used in this ‘dose of medicine’ context and not really outside it: “by mouth”. Wikipedia notes there is a Latin term:
It would not surprise me if the slightly odd phrasing in both English and Japanese was the result of a translation into “layman’s terms” of the Latin medical jargon at some point a couple of centuries back. (In the latter case, presumably via the Dutch.) Completely unfounded speculation, though
I think you’re running up against the limits of trying to translate parts of speech directly into english here. the (admittedly unsatisfying) answer is that it’s から and not で because から is the appropriate particle when you’re speaking japanese…
で tells you where or how an action is happening, but 飲む implies there’s a motion from the mouth to inside the body (weblio defines it as「 飲食物を口から体内に送りこむ。」). contrast that with 「口で噛む」(chew in the mouth), or 「歯で噛む」(chew with your teeth) which works because the action of chewing takes place in your mouth/using your teeth for its entire duration.
if you have to translate, “from” feels the most appropriate to me here, because it seems to fit how から is used in similar contexts better (and the above definition of 飲む). this interpretation fits the pattern of 「〈玄関・窓〉から（家に）入る」 as well. really though, that’s splitting hairs.
I think rather than being medicine specific, it’s just that medicine is one of the few contexts where it might be important to specify how you 飲む something.
Yes, there are cases (including the OP) where you can use ‘via/through’ and it’s the only sensible translation; there are some where either ‘through’ or ‘from’ happen to work in English. My point is not to think simply that から means only “via, through”, because that will lead you astray – it has also the ‘starting point’ meaning, and that is more common. パーティーは6時から始まります does not in any way mean “the party is via/through 6 o’clock”, not even in a “literal translation”.