Of high school seniors in 2001, 8.2% reported having ever used cocaine. Many scientists had attempted to isolate cocaine, but none had been successful for two reasons: the knowledge of chemistry required was insufficient at the time, and the cocaine was worsened because coca does not grow in Europe and ruins easily during travel. Men and women who smoked marijuana before age 17 are 3.5 times as likely to attempt suicide as those who started later. As with other amphetamines, tolerance to methamphetamine is not completely understood, but known to be sufficiently complex that it cannot be explained by any single mechanism. The extent of tolerance and the rate at which it develops varies widely between individuals, and even within one person it is highly dependent on dosage, duration of use and frequency of administration. Many cases of narcolepsy were treated with methamphetamine for years without escalating doses or any apparent loss of effect. | 
