Marijuana 8 years prior (Estimation to when you would be apolying for a job) won't be an issue for MOST agencies. A majority of people who suffer from ADD grow out of it, or at least learn to deal with it without medication by their late teens, early 20's.
Cronic depression (Bi-Polar) could be a problem. Depression already runs high in law enforcement. If you're already prone to it and taking medication, that may make a lot of agencies a little skittish. You don't say how old you are now, but I'm guessing you were refering to high school, so I assume you're in your teens. You may outgrow the depression problems too. You still have a long way to go before you can apply. I suggest you do as the others have suggested. Stay away from the dope, choose your friends wisely, and keep your nose clean. When you reach 21, re-evaluate your ADD and depression. If you're not ready, wait 5 years and re-evaluate again. Just because you are not ready the day you turn 21, doesn't mean you can never be ready.
"The answer to this last question will determine
whether you are drunk or not. Was Mickey Mouse a cat
or a dog?"