I've known a lot of weed addicts over the years. Watching my older brother and his friends for the last 20+ years is all the proof I need. When you can't function for more than a couple hours without toking again, can't go anywhere without bringing your weed, get angry if you don't get to toke regularly, or are blowing up your marriage because you can't stop. Then you are addicted.

I had roommates that on payday would go buy some weed and smoke non stop. They would always run out well before the next payday. I would watch them scrape the burnt resin out of all of their pipes & bongs just to get one more toke. Then they'd be trying to borrow or scrounge up any money they can to buy more. It wasn't until after they were forced to stop smoking that they finally admitted there was a problem.