Drinking and drug use begin early for many young Americans. A new study shows that by the time most teens reach late adolescence, most of them have consumed alcohol and abused illicit substances.

The study, published in the Archives of General Psychiatry, revealed that 78 percent of U.S. teens had consumed alcohol, and 47 percent of the group said they'd had 12 or more drinks in the past year. When it came to drug use, 81 percent of teens said they had the opportunity to use illicit substances, with 42.5 percent actually tried them.

A disturbing finding was that 15 percent of the teens met the criteria for lifetime alcohol abuse, and 16 percent could be categorized as drug abusers. The median age for alcohol abuse to begin was 14 with or without dependent behavior. The median age for drug abuse with dependence to start was at the age of 14 and teens who started abusing illicit substances at 15 were less likely to be dependent.

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