Is it possible to overdose from taking too much hydrocodone a.k.a. Loratab 10's

I recently read an article that accidental overdoses from mixing perscription drugs seem to be rising over the last 10yrs. For example with the recent death of Heath Ledger, the actor from the Dark Knight, he mixed hyrocodone, and zanax. I also had a cousin a few years ago who overdosed from the same thing, mixing 2 different RX pills. So I know that mixing 2 different pills can be deadly, but can taking just 1 be just as deadly?I have someone who is close to me who takes an abusive amount of hydrocodone daily and I dont want this to happen to him.