(HealthDay News) -- - Parents are largely unaware of their children's alcohol and drug use, new research says.

In a study published in the October issue of Alcoholism: Clinical & Experiemental Research, researchers from Washington University in St. Louis sought to determine how helpful parents are in assessing their children's alcohol and drug use.

The researchers interviewed 591 adolescent-and-parent pairs about the teens' use of alcohol and drugs.

"The three most commonly used substances as reported by adolescents in our study were alcohol at 54 percent, tobacco at 44 percent and marijuana at 23 percent," Jean Bierut, associate professor of psychiatry at the university's school of medicine, said in a prepared statement.

But when the child reported alcohol or drug use, the parents often failed to report that their child had used a substance.

"Specifically, if a child reported having used alcohol, the parent said their child had used alcohol only 50 percent of the time. Similarly, when a child reported having used tobacco, the parent reported this on 55 percent of the time, and when a child reported having used marijuana, the parent report agreed only 47 percent of the time," said Bierut.

The older the child, the more likely the parent was aware of the substance use.

"This is very troubling because research has shown that starting to use alcohol and drugs at a young age is a risk factor for developing substance abuse or dependence in the future," Bierut said.