MONDAY, Oct. 25 (HealthDay News) -- Don't expect teens -- or their parents -- to be honest about their drug use, a new study shows.

Researchers often survey teens to determine the extent of drug use, but this new research finds that respondents frequently lie even if they know they'll be tested for drugs or they're told the results will be confidential.

The findings are important for pediatricians to understand, said study lead author Dr. Virginia Delaney-Black.

"If you think it's important to know whether a kid is doing drugs -- specifically heroin, prescription pain killers or cocaine -- then don't rely on what the teens report," she said.

Perhaps some folks don't trust the confidentiality agreement; others may think their behavior is no one else's business or they may fear reprisal. "Many of us feel that this kind of personal information is personal, and that we don't have to tell other people what the truth is," said Delaney-Black, a professor of pediatrics at Children's Hospital of Michigan.

For this study, researchers surveyed more than 200 teens and 200 caregivers -- 80 percent were mothers -- about their drug use and then analyzed their hair for at least one drug. The participants were black, poor and from an inner-city urban area.

The study findings, reported in the November print issue of the journal Pediatrics, were published online Oct. 25.

No teens said they'd recently used opiates such as heroin or prescription painkillers, but the hair tests showed that nearly 7 percent had. Among parents, 3 percent admitted using opiates while testing revealed use by 7 percent.

About 1 percent of teens reported recent cocaine use, while testing revealed the actual number was about one-third. Hair analysis showed 28 percent of parents had used cocaine but only about 6 percent admitted it.

It's possible that the hair tests indicated drug use when a person was actually only around people who used drugs, Delaney-Black said. But, in essence, what the teens and parents said about their drug use was "very misleading," she said.

Parents also tended to under-report their teenagers' substance abuse, leading the researchers to conclude that health-care providers should rely on other methods, such as drug testing, rather than self-reports or parents' reports to identify at-risk teens.

Previous studies looking into teens' truthfulness about their drug use appear to have looked only at kids in drug treatment or in the court system, Delaney-Black said.

Ty S. Schepis, an assistant professor of psychology at Texas State University at San Marcos, said the study "generally reinforces what we know from work in adults, which is that people are usually less honest about substance use than we hope."

People are reluctant to tell researchers, or almost anyone for that matter, that they participate in illegal or undesirable activities, he said.

"Even if it means lying, people often like to present themselves in a favorable light," he added.

More information

The U.S. National Library of Medicine has more on teens and drug use.