The earlier a young person uses marijuana the greater the risk for mental health problems later in life, the director of National Drug Control Policy said Tuesday, basing his conclusion on a survey of medical research.

“We’re trying to get out the word that the last 10 years of research have helped to alert us to the use of marijuana in particular is a very dangerous risk for the mental health of our young people,” John Walters said at a news conference.

He said the conclusion runs against popular culture that often considers marijuana a low-risk recreational drug.

Walters cited a government study that found a base rate of mental illness at between 8 percent and 9 percent among Americans 18 and older. For those who use marijuana, he said, “That increases to 12-and-a-half percent.”

And, he added, “For those who have used marijuana prior to age 12, the rate of mental illness jumps to 21 percent.”

The rate was half that, or 10.5 percent, for adults who first used marijuana at age 18 or older.

Those were the findings of the National Survey on Drug Use and Health, an annual survey sponsored by the Substance Abuse and Mental Health Services Administration.

Walters did not directly address the possibility of confusing cause and effect - that is, that people with mental problems might be more inclined to use drugs.

One study he cited was published last year in the Archives of General Psychiatry. It involved 600 pairs of same-sex twins, one of whom was dependent on marijuana and one of whom was not. The twin who was dependent was almost three times as likely to think about suicide and attempt suicide than his brother or sister, the study found.

Neil McKeganey, who heads the University of Glasgow’s Center for Drug Misuse Research, was at the press conference in support of Walters.

“It is leading us to look again at this so-called recreational drug,” he said. “Kids who start to use marijuana at a young age are much more likely to suffer serious, long-term mental health problems.”

The parents of a teenager who committed suicide last year were also at the news conference, and they linked their son’s death to his marijuana use.

Tanya Skaggs, of Colorado Springs, Colorado, said, “He had a severe lack of judgment that was because of the marijuana, this destructive behavior was continuing,” in the months leading up to his death.

The parents were unable to break his marijuana use, Skaggs said, despite counseling, searching his room for pot and random drug tests.

“We just never thought that something like this could happen to us. But it does, and it did,” she said. “We wish we could have helped.”