That's what happens when you fark about with heroin. What usually happens is that once the door is opened to it, it can come calling any time it likes. The user understands the damage it does so quits. The body's coping mechanism relaxes as it's not being bombarded by the drug, brown sugar comes a-knocking, the user can't resist the knock, goes back at the dose s/he was formerly using without bothering titrating up to that amount and kapow - overdoses. I personally knew eleven people that happened to in exactly that way and know about so many famous ones it happened to like that, Gram Parsons being the obvious example.