In some parts of the world they conjure wild memories from the 2010s. In Russia, they're more popular than weed.When a group of powerful, legal stimulants burst onto the drug scene in the UK and U.S. a decade ago, they caused a media frenzy. In Britain, mephedrone came virtually out of nowhere in 2009 to become a hugely popular drug with university students, clubbers and rural teenagers. Dubbed "meow meow" by newspapers and sold online as “plant food,” it was the “killer” drug that made people rip off their own scrotums. Yet behind the hype, to young people using it,...