Next airing Sun Dec 13, 3 a.m. ET

San Francisco Meth Zombies

San Francisco, Calif. ' the epicenter of the 1960s' psychedelic revolution ' is notorious for drugs. But in the new millennium, the city, especially the gay community, is struggling to recover from a meth epidemic. The enabler of this situation is the Asian cartel, which has been poisoning San Francisco with high quality meth for almost 25 years ' but the Mexican cartels are intent on taking over. Nat Geo goes inside one of the worst drug ghettos in America ' the heart of the drug trade.