How broad is the meaning of 薬?


I saw on a board the other day someone referring to insecticide as "薬", which
doesn't really fit with the English conception of "medicine". I looked up "薬"
in Kenkyuusha, and sure enough, "chemical" was listed as a meaning (along with
"enamel", which is just weird if you ask me, but anyway . . .). My question
is, how broadly does the "chemical" sense apply in normal usage? For example,
would an adhesive,a cleanser, or a solvent be classed as "薬"? Additionally,
are there other senses which might surprise an English speaker?




If you pronounce it くすり, then it basically exclusively refers to something
that will have a positive effect on living beings (primarily therapeutic but
also in a more lax manner). In a strict sense くすり will be material, but it can
also be used as a metaphor:  
Note: I wrote くすり for illustrative purpose, but normally it is written as 薬.

[code]

     このくすりを呑みなさい (therapeutic)
     スパイスはくすりにもなるのでたくさん食べましょう ("good for your body")
     歩道でスケートボードしてて骨折か。まぁ、いいくすりになったんじゃないの？ (metaphoric)
     水槽にくすりを入れてあげなさい (to non-humans)
    
[/code]

Metaphorically, it can be applied to non-living things as well, but it must
have an positive effect: 日本経済に処方するくすりとなるか？

When it's pronounced やく, it's basically exclusively used in conjunction with
other kanji, as in 薬品、爆薬、薬量、薬価 etc. etc. Here it can more broadly refer to
chemicals. If you are a chemist, a cleaner may well be a 薬品. If you are a
layperson, to call an ordinal cleaner "薬品" sounds a bit odd. If it's some kind
of an potent, special cleaning agent or something, then ppl use 薬品. I guess
that's similar to English.

You might hear the word "ヤク", which I believe comes from 薬. This is
exclusively a slang for entertaining drugs (basically illegal drugs).




If you pronounce it くすり, then it basically exclusively refers to something
that will have a positive effect on living beings (primarily therapeutic but
also in a more lax manner). In a strict sense くすり will be material, but it can
also be used as a metaphor:  
Note: I wrote くすり for illustrative purpose, but normally it is written as 薬.

[code]

     このくすりを呑みなさい (therapeutic)
     スパイスはくすりにもなるのでたくさん食べましょう ("good for your body")
     歩道でスケートボードしてて骨折か。まぁ、いいくすりになったんじゃないの？ (metaphoric)
     水槽にくすりを入れてあげなさい (to non-humans)
    
[/code]

Metaphorically, it can be applied to non-living things as well, but it must
have an positive effect: 日本経済に処方するくすりとなるか？

When it's pronounced やく, it's basically exclusively used in conjunction with
other kanji, as in 薬品、爆薬、薬量、薬価 etc. etc. Here it can more broadly refer to
chemicals. If you are a chemist, a cleaner may well be a 薬品. If you are a
layperson, to call an ordinal cleaner "薬品" sounds a bit odd. If it's some kind
of an potent, special cleaning agent or something, then ppl use 薬品. I guess
that's similar to English.

You might hear the word "ヤク", which I believe comes from 薬. This is
exclusively a slang for entertaining drugs (basically illegal drugs).

