
“Biker meth” is most if not all meth now. It uses phenyl-2-propanone as the starting point and produces a racemic mixture of dextromethamphetamine and levomethamphetamine.
Traditional clandestine meth production using ephedrine produces pure dextromethamphetamine.
d-methamphetamine is the euphoric feel good stuff. l-methamphetamine is the racing heart, more neurotoxic, nearly immediate psychosis stuff.
TL;DR - “Biker meth” is most meth now. It’s much worse for you and less enjoyable.
Just tighter controls on ephedrine and pseudoephedrine. Any dumbass can make it in the bathroom easily with homemade lab equipment using ephedrine, so a lot of law and law enforcement crackdowns have centered on that.
I haven’t seen the show in a long time and never finished it, but from what I remember, later in the show they ditch both methods and move on to methylamine. Going that route would also allow production of isolated d-methamphetamine.