What I meant was that the drugs are "clean", not tainted with impurities that might blow out a part of your neural circuit or otherwise poison the user.
There was a book published a few years back, "The Case of the Frozen Junkies." These dopers turned up stiff as boards, though alive. They found out later that they were fully conscious but could not move because their Substantia Nigra in their brain stem no longer manufactured dopamine, necessary for voluntary muscle movement. This was one of the first stem cell implant cases; stem cells were placed in the substantia nigra in hopes that dopamine production would come back.
Imagine the hell of being frozen, while fully awake. But that's what you risk with home-made drugs.
You take enough of any kind of drug and it could have the capability to 'cook' you...