The dramatic rise of antipsychotic prescribing in youth occurred in conjunction with the illegal marketing of the drugs by their makers, resulting in multibillion-dollar settlements with the government

Since 1993, the rate of antipsychotic drug prescribing to children increased by a factor of nearly eight, while prescribing to teens quintupled and in adults nearly doubled, according to a new study.

Virtually all of this growth was seen in prescriptions for second-generation, or so-called atypical antipsychotic medications, which are often dispensed off label — meaning the drugs are prescribed for conditions that they are not specifically approved by the government to treat. Once a drug is allowed on the market, however, doctors are at liberty to use the drug for other conditions: antipsychotics were originally approved to treat schizophrenia and bipolar disorder, but these disorders are uncommon in adults and even more rare in children.

There is much evidence that the vast increases in atypical antipsychotic prescribing in recent decades were fueled by the aggressive marketing tactics of drug companies. In recent years, every major manufacturer of atypical antipsychotics has been involved in the illegal marketing of the drugs (while doctors can prescribe drugs off label, it is against the law for drug makers to market them for off-label uses), each ultimately paying hundreds of millions to billions of dollars in fines for their sales and marketing tactics. The settlements with the U.S. government were among the largest in history.

(MORE: Drugging the Vulnerable: Atypical Antipsychotics in Children and the Elderly)

In June, for example, Johnson and Johnson reportedly agreed to pay up to $2.2 billion for illegally promoting a variety of drugs, primarily the atypical antipsychotic Risperdal — and even that giant settlement with the government doesn’t resolve several other state lawsuits against the company, seeking billions more, for related offenses. In 2009, Eli Lilly was similarly made to pay $1.4 billion in fines related mainly to the illegal marketing of its antipsychotic drug Zyprexa — $615 million of that to settle criminal charges. Further, as we reported last year:

The charges against Lilly involved selling Zyprexa to doctors for use in children, despite the fact that it was not approved for this age group. Bristol Myers Squibb paid $515 million in 2007 to settle charges that it also illegally pushed its antipsychotic Abilify to child psychiatrists. Pfizer paid out $301 million in a similar case related to its drug Geodon. AstraZeneca paid out $520 million to settle charges over the drug Seroquel. In all of these cases, the drugs were sold for unapproved use in youth.

The new study , published in the Archives of General Psychiatry, found that in 2005-09 nearly two thirds of all antipsychotic prescriptions for youth were written for ADHD and other disruptive behavior disorders; these conditions accounted for 34% of all antipsychotic prescriptions for teens. Yet there is little data supporting the safety or efficacy of the drugs for those conditions. The drugs’ effect on children’s brain development is also not known, but their side effect profile is clear: aytpical antipsychotics are known to cause weight gain and diabetes, side effects to which children seem particularly prone.

“As the actual evidence base that would support [such off-label prescriptions of antipsychotics] is scant to non-existent, and the evidence of permeating undue influence of pharma on prescribing practices in psychiatry is abundant, one is led to the conclusion that this is another example of irrational prescribing that can be traced to both the overt and tacit influence of [drug companies] on practitioners,” says Dr. Bruce Perry, a senior fellow at the ChildTrauma Academy. [Full disclosure: Perry and I have co-authored two books.]

Perry testified for the state of Texas in a case that resulted in a $158 million settlement with Johnson and Johnson in January to resolve claims that it fraudulently marketed Risperdal and swindled the state’s Medicaid program. One aspect of the case involved misleading claims about the drug’s effectiveness for behavior disorders in children.

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The new Archives study examined thousands of medical records in the National Ambulatory Medical Care Surveys, comparing antipsychotic prescribing rates in 1993-98 to those in 2005-09. It found that while, on a population level, adults received more prescriptions for antipsychotics from their doctors than did children or teens, the rate of prescription is skyrocketing in younger patients. By 2005-09, the proportion of youth and adult visits to psychiatrists involving antipsychotic prescriptions were roughly equal: 31% and 29%, respectively.

The authors conclude: “In light of known safety concerns and uncertainty over long term risks and benefits, these trends may signal a need to re-evaluate clinical practice patterns.” The authors also call for more clinical trials of antipsychotics’ effect on conditions they are already being used to treat.

The study was funded by the Agency for Healthcare Research and Quality, but some of the authors reported prior funding from industry.

Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.