Early research is raising concerns about the drug Ritalin (search), suggesting that children who take it may have an increased risk of cancer.

All 12 of the children included in the study experienced an increase in chromosome abnormalities three months after starting Ritalin. Chromosome damage has been linked to heightened cancer risk and to other health problems.

While potentially alarming, researchers say much larger studies are needed to confirm the preliminary findings.

“Nobody is saying that because a child takes Ritalin he or she will develop cancer,” toxicologist and senior investigator Marvin Legator, PhD, tells WebMD. “There is nothing certain about this yet, but this is potentially a very large risk factor.”

50 Years of Use

Ritalin is a stimulant widely prescribed for the treatment of attention deficit hyperactivity disorder (search) (ADHD), with roughly 10 million prescriptions filled each year in the United States. The amphetamine-like drug has been approved for more than five decades. But sales of Ritalin and chemically similar drugs increased by more than 500 percent in the 1990s.

Several animal studies have suggested a link between Ritalin use and cancer, but there has been no evidence linking long-term use of the drug to human cancers.

The newly published study is the first to examine the chromosome-damaging potential of Ritalin. It will be published in an upcoming issue of the journal Cancer Letters.

Researchers from the University of Texas M.D. Anderson Cancer Center in Houston and the University of Texas Medical Branch at Galveston recruited a dozen children with ADHD for the study. The children were about 8 years old and had been prescribed Ritalin at normal therapeutic doses (20-54 mg/day) but had not begun taking it.

Blood samples were taken from the children before and three months after starting Ritalin. White blood cells were tested for chromosomal damage using several testing methods.

Lead researcher Randa A. El-Zein, MD, PhD, and colleagues found a threefold increase in the level of chromosomal damage in the samples taken after the children were started on Ritalin.

“It was pretty surprising to me that all of the children taking [Ritalin] showed an increase in chromosome abnormalities in a relatively short period of time,” El-Zein says.

Why Are Some Experts Skeptical?

Oncologist Herman Kattlove, MD, tells WebMD he remains skeptical about a link between Ritalin and cancer, noting that chromosomal damage and repair is common. Kattlove is a spokesman for the American Cancer Society.

“We all have chromosomal breaks,” he says. “That is part of the normal behavior of a cell. But fortunately, we have repair mechanisms which keep us from getting into trouble.”

Kattlove says the study does raise questions about Ritalin and other drugs of its class that should be investigated further.

“It is very unlikely that this would be a source of cancer in humans, but since this question has been raised it would be worthwhile to do a clinical study,” he says.

Pediatric oncologist Stephen A. Feig, MD, agrees that the risk, if any, is likely to be small.

“We don’t know if this is of any clinical significance, because we don’t know if the cells are repairing themselves,” he tells WebMD. “It seems that in the 50 years that Ritalin has been on the market an increase in cancer risk would be obvious.”

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: El-Zein, R. Cancer Letters, 2005. Randa A. El-Zein, MD, PhD, department of epidemiology, University of Texas M.D. Anderson Cancer Center, Houston. Marvin S. Legator, PhD, professor and director, division of environmental toxicology, University of Texas Medical Branch, Galveston. Herman Kattlove, MD, medical oncologist; spokesman, American Cancer Society. Stephen Feig, MD, professor of pediatrics, division of hematology-oncology, UCLA Jonsson Comprehensive Cancer Center, Los Angeles.