The fact remains that in most places amphetamines are an illegal drug when acquired without a prescription.

I think he should just rebrand. A name change is not a big deal, given the app has low name recognition in the first place. News of the rebrand will be the first Google result for people who are unaware of it.

Apple holds all the cards here. There is little to be gained if he wins, and if he loses he will have to rebrand anyway after much wasted effort.