Hey there,
Concerning the weight loss, it hasn't happened to me personally (at least not yet, in any discernable amount), but I think it does happen for some people, as a combination of the following things:
1) Nal sometimes makes one nauseous or unable to eat/drink large amounts in one sitting. (For me it sometimes makes me vomit eeep). This is usually only at the beginning, however.
2) Nal makes people drink less and be more in control of their drinking, which leads to a) fewer calories drank and b) fewer late night pizza binges

3) Being AF or not hungover more often, people tend to work out more and eat healthier on TSM.
I don't think, however, that Nal itself is a stimulant/appetite suppressant in the strictest sense. Hope this helps.
EL