The first study was from Beckman Institute at the University of Illinois. Dr. Justin Rhodes and his colleagues found that adolescent mice were less sensitive to the effects of cocaine and methamphetamine than adults. The adults showed more increases in locomotion, but the drugs had little to no effect on the "teenagers." Dr. Rhodes was unsure why this occurred.

Dr. Rhodes said that a young person’s first experiment with cocaine and methamphetamines may be extremely mild, which in turn would increase the likelihood of his or her using drugs again.

"If you have a strong reaction to something, then you are less likely to do it again," Dr. Rhodes said.

This study appears in the journal Neuroscience.

The second study was from the University of Valencia. Dr. Jose Minarro found that mice given ecstasy and cocaine during adolescence developed a vulnerability to them in adulthood. The control group of mice that had not been exposed to drugs in adolescence had less vulnerability.

"Adolescence is a critical stage during which time drug consumption affects plastic cerebral processes in ways that cause changes that persist right through adulthood," according to Dr. Minarro in a report published in the journal Addiction Biology.

Half of the 21-year-olds in the study reported having used cannabis in their lifetime, and 21 percent were classified as having a cannabis use disorder. Males were much more likely than females to have experienced cannabis abuse or dependence.

Children whose mothers frequently changed their marital status or who experienced sexual abuse at childhood were more likely to develop a cannabis use disorder by 21 years.

Those who showed aggressive or delinquent behavior at 14 years were more than twice as likely as other children to develop a cannabis use disorder by 21 years. Young adults who reported poor academic performance or had smoked a cigarette or consumed alcohol by 14 years were more likely to use and develop a cannabis disorder than others who had not.

Dr. Reza Hayatbakhsh, a researcher at the Queensland Alcohol Drug Research and Education Centre at UQ’s School of Population Health and lead author of the paper, believes that the study is a breakthrough for policy makers and health professionals.

“The majority of those who experience a cannabis disorder by 21 years of age are at moderate to high risk, based upon our data,” Dr. Hayatbakhsh said. “Policy makers could focus on addressing the health needs of young persons with aggressive or delinquent behavior, to limit the tobacco use of young people, and to the prevention of childhood sexual abuse.”

“Clinicians and health workers treating cannabis-related problems should consider the individual’s background as a possible contributor not only to their use of cannabis, but factors which may continue to limit the effectiveness of a treatment program,” Dr. Hayatbakhsh continued.

The study is based on the Mater-University Study of Pregnancy, Australia’s largest longitudinal study, which has tracked more than 8,000 mothers and their children over a 21-year period.

Science Daily reports that researchers at the Boston University School of Public Health, Johns Hopkins Bloomberg School of Public Health, and Virtual Media Resources who conducted the study (published in this month’s issue of the Journal of Adolescent Health) say their findings present the strongest evidence to date that alcohol companies are targeting youths through magazine advertising.

They note that three major trade associations representing the alcoholic beverage industry—the Wine Institute, the Beer Institute, and the Distilled Spirits Council of the United States—have publicly stated that they do not advertise to underage youths.

"Alcohol companies are deceiving us," said Dr. Michael Siegel, professor of community health sciences at Boston University School of Public Health and a co-author of the study. "Contrary to their public statements, they are targeting youths through their advertising. They are saying one thing, but doing another."

The study compared alcohol advertisement placements in 118 magazines from 2002 to 2006, specifically looking at the relationship between a magazine’s youth readership and the probability of youth alcoholic beverage types—defined as those consumed by a large proportion of youth—being advertised in each magazine.

The researchers found that in magazines with the highest levels of youth readership, youth alcoholic beverage types (e.g., premium beer, low-calorie beer, rum, vodka, and flavored alcohol beverages) were more than four times more likely to be advertised than non-youth types (e.g., gin, brandy, whiskey, and scotch). As youth readership increased in a magazine, so did the number of youth alcoholic beverage advertisements.

The researchers identified a total of 13,513 alcohol advertisements in the 118 sample magazines during the five-year study period. While 23.1% of advertisements for non-youth/adult alcoholic beverages appeared in magazines with high youth readership, 42.9% of advertisements for youth alcoholic beverage types were placed in the same magazines.

"The percentage of a magazine’s youth readers was an important predictor of which alcoholic beverages were advertised in a magazine," the authors said.

The researchers noted that previous studies examining the issue of targeted advertising were limited by the problem of "lumping together types of alcohol that are and are not consumed frequently by underage youths." In this study, the researchers used 2006 data on alcohol use among 18- to 20-year-olds that was collected as part of a large national survey called the Survey of the American Consumer.

The study notes that in 2005, the alcohol industry spent $4 billion overall in advertising and promotion. The authors wrote: "The question of whether this advertising is disproportionately reaching and influencing underage youths (under 21 years old) lies at the heart of the public health debate about interventions to reduce youth drinking.”

Marijuana is the most widely used illicit drug by adolescents, with almost 42% of high school seniors admitting to having experimented with it. Continued marijuana use may result in a number of serious consequences including depression, cognitive impairment, cardiovascular disease, and certain forms of cancer. It is critical to prevent marijuana use by adolescents, and numerous behavioral and medical scientists have been trying to establish the best means of prevention.

Many studies have focused on parents as being the best avenue for preventing adolescent marijuana use. Parental monitoring (when the parents know where their children are, who they are with, and what they are doing) has been seen as attenuating a number of negative adolescent behaviors, including gambling, sexual activity, and drug use. However, the strength of the relationship between monitoring and marijuana usage has been unclear; for example, if adolescents use marijuana, they may be more likely to hide that from their parents, compared to other behaviors. Despite this uncertainty, millions of dollars are spent annually on programs and media campaigns that urge parents to monitor their children’s behavior.

Psychologists Andrew Lac and William Crano from Claremont Graduate University reviewed numerous studies to examine the connection between parental monitoring and adolescent marijuana use. For this review, Lac and Crano selected 17 studies from the literature, which contained data on more than 35,000 participants. Criteria the researchers used for selecting studies included using adolescent participants, focusing exclusively on marijuana, and evaluating monitoring by adolescent self-reports, not parents’ reports of their own monitoring behavior.

Results of this comprehensive analysis, reported in the current issue of Perspectives on Psychological Science, a journal of the Association for Psychological Science, reveal that there is in a fact a strong, reliable link between parental monitoring and decreased marijuana usage in adolescents. In addition, the strongest effects were seen in the female-only studies.

The authors note, “Our review suggests that parents are far from irrelevant, even when it comes to an illegal and often secretive behavior on the part of their children.” They conclude that the information gleaned from this analysis may be useful for marijuana-based prevention programs that target parents and might provide some insight into alleviating risky adolescent behavior.