春药 (aphrodisiac / chūnyào) is a substance that increases sexual desire. Examples of natural aphrodisiacs are ginseng, chocolate, and deer penis (at least in China today).
Why it is blocked: Even though China has a long history of using aphrodisiacs (purportedly even emperors relied on them to satisfy their harem of concubines), certain discussions about improving one’s virility are apparently taboo (however, 伟哥, aka Viagra, is not blocked). Perhaps this is a public safety measure, what with reports of older sex pill-popping Lotharios dying after engaging in too vigorous sex (in Jin Ping Mei, one of China’s most famous novels, a character dies of an accidental overdose of aphrodisiac pills). There was also a strange rumor in 2011 that an aphrodisiac made of dead babies was being sold in China. [Status (along with 媚药) - 11/26/11: blocked; 2/5/12: blocked]