Lyric discussion by misshopestar 

Cover art for Chemical, Chemical lyrics by Pretty Girls Make Graves

I agree with lol_is_a_lie but I think it goes beyond prescription drugs. I think its a more general concept of drug use, legal or not, to numb certain unwanted feelings.

I think it's also talking about how when you act a bit out of the norm they automatically "numb" you out.

"He's got a secret to tell His imaginary friend knows everything Don't let him go out"

He is acting a bit different, thus we have to "control him" maybe kind of touching on the point of copy cat effects, like if we dont control him he will infect others? (because of the "dont let him go out"