I’ve heard “on crack” used similarly to “on steroids,” as an American English speaker. For example, it would not be out of the question to say something like “

I’ve heard “on crack” used similarly to “on steroids,” as an American English speaker. For example, it would not be out of the question to say something like “when the iPhone launched it was amazing. Like a palm pilot on crack.” So, when used positively, “on crack” is generally a modifier(in my experience). When used alone it does seem to have negative connotations.