ADHD Drugs Don't Cause Genetic Damage

Nov. 19, 2008 -- Ritalin, Adderall, and Concerta do not appear to cause genetic damage in children who take them for attention deficit hyperactivity disorder (ADHD), a new government-funded study concludes.

The findings should reassure parents concerned that the stimulant drugs used to treat ADHD may be linked to an increased risk of cancer.

Those concerns were raised by a 2005 study showing evidence of drug-related chromosomal damage in 12 out of 12 children with ADHD taking Ritalin.

The new study, conducted by researchers from the National Institutes of Health and Duke University Medical Center, shared a similar design with the earlier trial.

But it was larger and also included children taking Adderall and Concerta.

"We saw no [chromosomal] effect associated with medication in any of our treatment groups," genetic toxicologist and researcher Kristine L. Witt, MS, tells WebMD. "These findings were extremely reassuring."

ADHD Drugs and Cancer

Millions of children take either methylphenidate-based stimulants, like Ritalin and Concerta, or the mixed amphetamine stimulant Adderall for the treatment of ADHD symptoms.

Approved in 1955, Ritalin is the oldest and most widely studied ADHD drug. Adderall and Concerta have been sold in the U.S. for about a decade.

While a few animal studies have linked Ritalin use to tumor growth, the 2005 pilot study was the first human study to link Ritalin use to chromosomal damage that could promote cancer.

Subsequent studies examining the proposed link have not supported these findings.

In the current study, 47 children with ADHD between the ages of 6 and 12 took either Ritalin LA, Adderall, Adderall XR, or Concerta for three months.

Blood samples taken prior to starting the drugs and at the end of three months of treatment were assessed for chromosomal breaks, chromosome fragments suggestive of breaks, and exchanges of genetic material between pairs of identical chromosomes.

These three standard measures of chromosomal damage were the endpoints examined in the 2005 study.

But the outcomes in the two trials were very different.

"We did not see any significant treatment-related increases in any of these endpoints," Donald R. Mattison, MD, of the National Institute of Child Health and Human Development, says in a news release. "These results add to a growing body of evidence that therapeutic levels of these medications do not damage chromosomes."

Long-Term Safety of ADHD Drugs

ADHD expert Regina Bussing, MD, says the fact that the new study was publicly financed is a major strength. Bussing is a professor of psychiatry at the University of Florida, Gainesville.

"This was a high-quality study that was funded by the government, not the drug industry," she says.

Duke University ADHD program director Scott H. Kollins, PhD, who also participated in the study, says it is now clear that ADHD drugs do not cause chromosomal damage. But he adds that important questions remain about their long-term safety.

"We don't have a lot of information about long-term effects," he tells WebMD. "We need to follow patients on these drugs to address other concerns."

Concerns about the impact of long-term stimulant use on growth and later-life substance abuse have yet to be addressed, he says.

There are also suggestions that years of stimulant use during childhood might increase the risk for heart attacks and strokes during adulthood.

"We still don't know if treating a child for 15 years with these drugs will have a long-term impact on hypertension or other cardiovascular risk factors," he says. "We have no evidence that it will, but these studies have not been done."