A new multi-site study has found that children with attention deficit hyperactivity disorder (ADHD) are more likely to engage in substance use than youngsters without the disorder and had higher rates of marijuana and cigarette use going into adulthood.

The study's takeaway message, suggested lead author Brooke Molina, should be that parents of children with ADHD need to keep in touch with their children's activities and friends, even into the teenage years.

"They should keep their antenna up," said Molina, a psychiatry professor with the University of Pittsburgh School of Medicine.

In addition, the researchers say, routine health care providers should include early screening and intervention to help prevent substance abuse among ADHD youngsters.

The study, published in the current Journal of Child Psychology and Psychiatry, followed boys and girls with ADHD and their non-ADHD peers from six health centers in the United States and one in Canada, assessing them at regular intervals over 16 years. The average starting age for study participants was 10.

The researchers found about 58 percent of the ADHD group engaged in adolescent substance use, including alcohol, cigarettes, marijuana and other drugs, compared with 42 percent of the youngsters without ADHD.

Because of the findings, Molina said, more study is needed to learn how many young drinkers with ADHD have serious, chronic problems with alcohol as they get older.

In adulthood, the ADHD participants had slightly higher rates of weekly heavy alcohol use or monthly illicit drug use, while their cigarette smoking and marijuana use was significantly higher.

Weekly marijuana use was about 33 percent for the ADHD participants in their early adulthood years, compared with 21 percent of the non-ADHD study subjects. The difference in the daily cigarette smoking rate was even greater — about 36 percent for the ADHD adults and 17.5 percent for those without ADHD.

However, the study did have some hopeful findings regarding youngsters with ADHD, many of whom are prescribed stimulant medication.

Less than 2 percent of the study participants were misusing stimulants or using cocaine as young adults, Molina said.

"You would think they would go for drugs that are like the stimulant medication," she said. "The good news is, we're not seeing that."

Molina also said their research found that there is "no evidence their treatment increased their substance risk." However, the study authors suggest the increased risk of substance use may be due to ADHD and its symptoms – one of which is a tendency to be impulsive.

"Impulsivity has been shown for years to be a risk factor for substance abuse," Molina said.

In addition, some youngsters with ADHD, even if they are taking medication, may still have difficulties with school performance and social coping.

"Students and teenagers that don't do well in school tend to pull away from those conventional, healthily engaged activities we like to see our teenagers involved in," Molina said. "Then they are at risk for gravitating to more unhealthy activities that include drug and alcohol abuse."

More reasons for parents to continue to monitor their youngsters and keep in touch with their lives, the authors said.