One important discovery: evidence is building to support the 90-day rehabilitation model, which was stumbled upon by AA (new members are advised to attend a meeting a day for the first 90 days) and is the duration of a typical stint in a drug-treatment program. It turns out that this is just about how long it takes for the brain to reset itself and shake off the immediate influence of a drug. Researchers at Yale University have documented what they call the sleeper effect--a gradual re-engaging of proper decision making and analytical functions in the brain's prefrontal cortex--after an addict has abstained for at least 90 days.

• http://www.time.com/time/magazine/article/0,9171,1640436-2,00.html