Don't mean to derail but i'm a little late to the party. I'll be brief.
I guess every person is different, but personally, Marijuana is absolutely not addictive. Coffee was more addictive to me then MJ ever was, and I was a smoker for 11 years, with the last 3 of those years being 1.5 - 2 ounces of the highest quality available a week (I had a lot of bud at my disposal and went overboard on it just because I had it). I quit cold turkey one day and the only physical symptom I had was issues getting to sleep for 2 - 3 days. Nothing more then someone who quits coffee after a year or so.
As far as losing appetite, I actually gained my appetite back. When I was heavy into smoking I had no desire to eat anything or even think about food for at least the first 3 - 4 hours of the day. After 5 days off the MJ cold turkey, the moment I woke up I'd be craving food again immediately. I'd have to say MJ isn't physically addicting in any sense of the word. Potheads who say "they can quit at any time" easily could, they just choose not to. You lock them in a cell for a week and I guarantee you they wont be hunched over in a corner puking and going through withdraws.
As for adderall, personally Speed was never my thing. I was always about downers as opposed to uppers, but I knew a buddy who was heavily addicted to adderall for awhile. Downing 15 - 20 peaches (30mg addys) daily. To whoever said they took "one" and didn't feel it, you simply took a lackluster dose. Its not even subjective. 100% of the people, if they take a good enough dose, you WILL feel it, and feel it hardcore. Whether you consider that feel enjoyable or not is your opinion, but to say you took some before and simply didn't feel it just means you took a low dose. It's easily the same as saying you took the most minor hit of meth one could possibly take, and claim you can't see why its addicting and comparing that to people who smoke a gram of the stuff in one sitting.
A low enough dose of any drug on earth and I could easily not feel it, but to say addy, meth, coke, what have you, isn't addictive, it's foolish IMO.