Gateway to Nowhere? The evidence that pot doesn't lead to heroin. Earlier this month, professor Yasmin Hurd of the Mount Sinai School of Medicine released a study showing that rats exposed to the main ingredient in marijuana during their adolescence showed a greater sensitivity to heroin as adults. The wire lit up with articles announcing confirmation for the "gateway theory"—the claim that marijuana use leads to harder drugs. It's a theory that has long seemed to make intuitive sense, but remained unproven. The federal government's last National Survey on Drug Use and Health, conducted in 2004, counted about 97 million...
