Could ADHD Drugs Spur Development Changes? Higher Dopamine Receptors Found in Patients

Those with attention deficit/hyperactivity disorder (ADHD) who also take certain medications may experience periods of development changes in their brains that could ultimately impact their ability to respond to other drugs.

The study suggests that adults with ADHD have higher levels of a protein called a dopamine transporter in their brains after one year of treatment with the drug methylphenidate, (most commonly sold as Ritalin), compared with before they started taking the drug.

As researchers have speculated that people with ADHD naturally have more dopamine transporters in their brains, the new study also suggests that high numbers are a result of treatment with medications, said study researcher Dr. Gene-Jack Wang, of Brookhaven National Laboratory in Upton, N.Y. Prior to the study, none of the participants had ever been treated with ADHD drugs.

However, as the study only looked at patients over a one-year period, the consequence of this brain change is not known, according to Wang. Still, it's entirely possible that the change could affect the way patients respond to drugs. 

Dopamine is a brain chemical that sends signals between nerve cells, and is linked with attention and pleasure. It's thought that people with ADHD have problems with their dopamine signaling, and drugs like Ritalin work by increasing levels of dopamine, which helps patients focus.

Dopamine transporters, on the other hand, clear dopamine after the chemical has sent a signal. Thus, more dopamine transporters could mean that dopamine gets cleared more quickly, particularly during times when patients stop taking their medications.

The study involved 18 adults with ADHD who had their brains scanned twice: once at the beginning of the study before any drug treatment, and once at the end of the study after one year of taking Ritalin.

Among these participants, there was a 24 percent increase in the number of dopamine transporters in some areas of the brain. In contrast, a group of healthy participants who did not take Ritalin had no increase in dopamine transporters after one year.

"This could result in more severe inattention and the need for higher doses of medication," the researchers noted, regarding the study. 

However, they also indicate that future research is needed to explore whether this increase in dopamine transporters does in fact lead to higher tolerance of ADHD drugs.

The findings for the study are published in the May 15 issue of the journal PLUS ONE.