Michael Specter in The New Yorker:
The first thing people on methamphetamine lose is their common sense; suddenly, anything goes, including unprotected anal sex with many different partners in a single night—which is among the most efficient ways to spread H.I.V. and other sexually transmitted diseases. In recent surveys, more than ten per cent of gay men in San Francisco and Los Angeles report having used the drug in the past six months; in New York, the figure is even higher.
After years of living in constant fear of aids, many gay men have chosen to resume sexual practices that are almost guaranteed to make them sick. In New York City, the rate of syphilis has increased by more than four hundred per cent in the past five years. Gay men account for virtually the entire rise. Between 1998 and 2000, fifteen per cent of the syphilis cases in Chicago could be attributed to gay men. Since 2001, that number has grown to sixty per cent. Look at the statistics closely and you will almost certainly find the drug.