Study suggests ADHD drugs may affect male puberty

Ritalin is a common medication prescribed to millions of children diagnosed with attention deficit hyperactivity disorder, or ADHD. This a commonly diagnosed behavioral disorder in children. It is more common in boys and affects some 3 to 5 percent of school-aged children and causes symptoms such as over activity and inattentiveness.

The study was conducted on young rhesus monkeys under 5 years old. The monkeys were divided into groups with one receiving a low dose of methylphenidate, similar to the dose a human ADHD patient would receive, and the other group receiving a high dose, or 10 times what is used in humans. A separate control group was given only the material that the drug was dissolved in for the other monkeys but not the drug itself. These doses were administered over a 40-month time frame. The study was designed to evaluate possible toxic effects of the drug, such as DNA damage, so the effects they discovered were surprising.

The researchers, including Dr. Donald Mattison from the National Institute of Child Health and Human Development, discovered that testicular descent was significantly postponed in the monkeys that received the high dose of methylphenidate and lower blood testosterone levels and testicular volume were present in both sets of monkeys. The effects were not permanent and by the time the monkeys reached the age of 5, they were at similar stages of puberty compared to untreated monkeys.

Mattison cautions that it is too early to assume there may be clinical implications. This is a single study and more work needs to be done to see if it is repeatable. He warns that parents should speak with their child’s physician before making any changes to their medications and physicians should consider the possible effects of puberty when prescribing the medication.

More information: Pubertal delay in male nonhuman primates (Macaca mulatta) treated with methylphenidate, Published online before print September 19, 2011, doi: 10.1073/pnas.1102187108

Abstract
Juvenile male rhesus monkeys treated with methylphenidate hydrochloride (MPH) to evaluate genetic and behavioral toxicity were observed after 14 mo of treatment to have delayed pubertal progression with impaired testicular descent and reduced testicular volume. Further evaluation of animals dosed orally twice a day with (i) 0.5 mL/kg of vehicle (n = 10), (ii) 0.15 mg/kg of MPH increased to 2.5 mg/kg (low dose, n = 10), or (iii) 1.5 mg/kg of MPH increased to 12.5 mg/kg (high dose, n = 10) for a total of 40 mo revealed that testicular volume was significantly reduced (P < 0.05) at months 15 to 19 and month 27. Testicular descent was significantly delayed (P < 0.05) in the high-dose group. Significantly lower serum testosterone levels were detected in both the low- (P = 0.0017) and high-dose (P = 0.0011) animals through month 33 of treatment. Although serum inhibin B levels were increased overall in low-dose animals (P = 0.0328), differences between groups disappeared by the end of the study. Our findings indicate that MPH administration, beginning before puberty, and which produced clinically relevant blood levels of the drug, impaired pubertal testicular development until ∼5 y of age. It was not possible to resolve whether MPH delayed the initiation of the onset of puberty or reduced the early tempo of the developmental process. Regardless, deficits in testicular volume and hormone secretion disappeared over the 40-mo observation period, suggesting that the impact of MPH on puberty is not permanent.

© 2011 PhysOrg.com