It's a hard lesson to learn. I'm sorry your son is causing you and your parents heartache. But more than likely he won't be able to return the money and your parents would learn never to do that again.
I remember when my exah's parents once yelled at me for not giving him "enough" money (I had control over his paychecks). I exlplained to them why I was doing what I was doing and they said he still needs more money to live on. (Mind you his job was 5 min. away from home and his job would be complete within 4-5 hours so the rest of the day was spent hanging around until he had to sign out of work. And yes he was allowed to go home and eat and hang.) Now he lives with them and is doing to them what he had done to me. Result: They are giving him even less money I was giving him. Lesson learned.
But it doesn't stop him from drugging. I guess when there is a will there is a way.
My heart goes out to you and your parents.