As long as drugs are illegal, whichever drugs are easiest to make with legally-available materials will become popular, no matter how bad they are or what they're usually cut with.
Make drugs legal, and drug users will return to the classic drugs (pot/coke/opiates/hallucinogens). They'll only use other drugs if they provide a better high or less risk, which to my understanding meth does not.
“The egg hatched...” “...the egg hatched... and a hundred baby spiders came out...”
“Who are you?” “A friend. I'm here to prevent you from making a mistake.” “You have no idea what I'm doing here, friend.” “In specific terms, no, but I swore an oath to protect the world...”
“It's a goal you won't understand until later. Your job is to make sure he doesn't achieve the goal.”