Most adolescent drug addicts tested in a study of teen-age drug use took their first drinks at age 12 and smoked their first marijuana cigarettes six months later, according to preliminary results of research conducted by Louisiana State University. "It is by no means definite, but from the one-year study trends are emerging which confirm things which we've suspected all along," said Vern Ridgeway, director of Baton Rouge Hospital's Adolescent Chemical Dependency Unit. "The study shows a definite pattern of use. It outlines a classic addict profile, complete with a family history of addiction and specific behavorial problems. From alcohol and marijuana, the average adolescent user moves on to inhalants, downers and tranquilizers, speed, PCP, LSD, cocaine, opiates and heroin, the study concludes. The study shows that by age 12, some 98 percent of those entering the unit had smoked marijuana and 96 percent has used alcohol. By 16, the study said, 16 percent had used opiates and 13 percent had used heroin. The average amount of use ranged from a high of 25 times a month for marijuana to a low of three for LSD. More than 90 percent of those tested were classified as "being preoccupied with chemicals," meaning that their lives revolve around "getting high."