I don't have a dog in the fight since I'm no longer a Mac user and, when I was, I didn't use the app.
But, when I read the name, it didn't register as offensive to me. Amphetamines are a class of drugs and there are both legal and illegal ones...it doesn't immediately equate in my mind to crystal meth. But it does immediately equate to "keeps you awake", which seems appropriate.
It also seems a bit unfair after 6 years and 500k downloads. Had Apple made an issue of it originally, the author might have built all the goodwill and ratings with some other, more acceptable name.
The internet is a pretty big place to have to launch a product. Picking a name that suggests a purpose seems like a big win to me and coming up with a string of words that won't offend someone is a pretty big challenge these days.