I have to tell you I am not sure that adderall "speeds up your metabolism". I have just read some stuff that says it does but am not sure of that. I know it stimulates your central nervous system but don't think this is the same thing as say doing an hour of cardio. There are different formulations for adderall depending if it is generic or not. Here is an article on it ..http://en.wikipedia.org/wiki/Adderall
That being said one of the effects of adderall can be loss of weight but I think that is more because it can suppress appetite. I used to take adderall XR but stopped because it made me moody. I did better with the generic 30mg adderall that I could break into quarters and take as I needed during the day. Ironically it would make me hungry.
Right now I am not taking anything but sometimes take the natural supplement theanine (a derivative of tea). I have had thoughts of asking to try modafinilhttp://en.wikipedia.org/wiki/Modafinil
but it too has appetite suppressing effects.
One more thing. If you are like me you maybe just have problems putting on muscle. I think mine is part hormonal and part not eating enough (non-junk food). I have gained ten pounds of muscle in the last few months through just eating more (protein - mostly chicken and grains) and some various supplements, and working out harder.
I would not be averse to hormone supplementation if I could do it legally. You could have your testosterone levels checked. At our age there is just less there. If it is low you could get a legal prescription.