compulsive

Compulsive people have irresistible urges to do certain things, like a compulsive gossip who simply cannot keep a secret.

If you're compulsive, you can't stop yourself from doing something, like compulsive counting of the sidewalk blocks on your way to school. There is sometimes an upside to compulsive behavior — like a compulsive desire to be the best hockey player, which makes you work hard to make it happen. Someone who has compulsive tendencies can be called a compulsive, the noun form of the word.