In my experience ADHD medicine doesn't actually induce weight loss, despite weight loss being a desirable thing for me.

It suppresses your appetite, sure, but it doesn't shield you from the effects of not eating all day. I often force myself to eat something for lunch or I'll just end up tired and annoyed in the afternoon/evening (edit: I don't eat breakfast).

Plus, once the medicine wears off at night (or on weekends when I skip taking it), I usually get ravenously hungry and easily make up any caloric deficit.