|ADHD Medications Do Not Cause Genetic Damage
In contrast to recent findings, two of the most common medications
used to treat attention deficit hyperactivity disorder (ADHD) do
not appear to cause genetic damage in children who take them as
prescribed, according to a new study by researchers at the National
Institutes of Health (NIH) and Duke University Medical Center.
The study published online this month in the Journal of the American
Academy of Child and Adolescent Psychiatry (JAACAP) provides new
evidence that therapeutic doses of stimulant medications, such
as methylphenidate and amphetamine, do not cause cytogenetic (chromosomal)
damage in humans. The researchers looked at three measures of cytogenetic
damage in white blood cells of each child participating in the
study and found no evidence of any changes after three months of
"This is good news for parents," said Kristine L. Witt, M.Sc.,
a genetic toxicologist at the National Institute of Environmental
Health Sciences (NIEHS) and co-author on the study, which was funded
through the Best Pharmaceuticals for Children Act by NIEHS and
the Eunice Kennedy Shriver National Institute of Child Health and
Human Development (NICHD), both parts of NIH. "Our results indicate
that methylphenidate- and amphetamine-based products do not induce
cytogenetic damage in children."
The researchers involved emphasize that the findings should not
be interpreted as final proof of the long-term safety of stimulant
drugs for the treatment of ADHD. "More research and close monitoring
of children taking these medications for extended periods of time
is needed to fully evaluate the physical and behavioral effects
of prolonged treatment with stimulants," noted Scott H. Kollins,
Ph.D., director of the Duke ADHD Program, where the study was conducted
and a co-author of the paper.
ADHD is a disorder characterized by attention problems, impulsivity,
and hyperactivity. About 3 to 5 percent of children in the United
States have been diagnosed with the disorder, although several
studies suggest 7 to 12 percent of children may be affected.
The current study included 63 children, ranging from 6–12 years
of age, who met full criteria for ADHD but who had not previously
been treated with stimulant medications. Children in the study
were divided into two groups and treated by a board-certified child
psychiatrist with either methylphenidate (commercially available
as Ritalin LA and Concerta) or with mixed amphetamine salts (Adderall
and Adderall XR). Blood samples were taken before the medication
was started to establish baseline values for the cytogenetic measures
that were analyzed in the study, and a second sample was collected
after three months of continuous treatment. Forty-seven children
completed the full three-month treatment schedule.
The researchers found no significant differences between the two
groups of children with regard to age, gender, race, body weight,
height, or ADHD subtype. The groups also showed very similar ADHD
symptom levels at initial screening and children in both groups
responded equally well to the medication.
The researchers looked at three standard indicators of chromosomal
damage: structural chromosomal aberrations (breaks in chromosomes),
micronuclei (small nuclei consisting of chromosome fragments produced
by breakage or whole chromosomes lost from the main nucleus after
the cell divides), and sister chromatid exchanges (exchanges of
genetic material between a pair of identical chromosomes). "We
did not see any significant treatment-related increases in any
of these three endpoints," said Donald R. Mattison, M.D., senior
advisor to the director at NICHD. "These results add to a growing
body of evidence that therapeutic levels of these medications do
not damage chromosomes," he said.
The study was designed to determine the reproducibility of findings
from a previously published paper that reported methylphenidate-induced
chromosomal changes in children with ADHD. That paper raised concern
for the medical community and parents, given that some of the changes
have been associated with an increased risk of cancer. The current
study was not able to replicate the findings from the previous
study. The new JAACAP paper extends the literature by using a larger
sample size than previous studies, investigating more than one
commonly prescribed medication, and providing well-characterized
results that can be generalized to other ADHD populations.
"One way scientists evaluate each other's work is by attempting
to reproduce the original experiment or study," said Witt. "We
designed a study with specific modifications to address issues
raised with the original study. Thus, our results are based on
a significantly larger number of children who were carefully evaluated
using rigorous, accepted standards, which allowed us to produce
high-confidence data at the end of our study."
This study was supported by the NIH/NICHD Best Pharmaceuticals
for Children Act pediatric drug development program and the Intramural
Research Program of the National Toxicology Program at the National
Institute of Environmental Health Sciences. NIH Clinical Trial
The National Toxicology Program (NTP) is an interagency program
established in 1978. The program was created as a cooperative effort
to coordinate toxicology testing programs within the federal government,
strengthen the science base in toxicology, develop and validate
improved testing methods, and provide information about potentially
toxic chemicals to health, regulatory, and research agencies, scientific
and medical communities, and the public. The NTP is headquartered
at the NIEHS. For more information about the NTP, visit
The NIEHS supports research to understand the effects of the environment
on human health and is part of NIH. For more information on environmental
health topics, please visit our website at http://www.niehs.nih.gov.
The NICHD sponsors research on development, before and after birth;
maternal, child, and family health; reproductive biology and population
issues; and medical rehabilitation. For more information, visit
the Institute's Web site at http://www.nichd.nih.gov/.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and Centers
and is a component of the U.S. Department of Health and Human Services.
It is the primary federal agency for conducting and supporting basic,
clinical and translational medical research, and it investigates
the causes, treatments, and cures for both common and rare diseases.
For more information about NIH and its programs, visit www.nih.gov.