New research from Brookhaven National Laboratory suggests that methamphetamine enters the brain just as quickly as cocaine but spreads further and stays in the brain longer.

Researchers measured brain uptake, distribution, and clearance of methamphetamine in 19 healthy, non-drug-abusing men by injecting them with radioactively tagged forms of methamphetamine and cocaine in doses too small to have any psychoactive effects. Through brain PET scans, the authors tracked the concentration, distribution and number of dopamine reuptake proteins in each subject's brain.

The authors found that both drugs enter the brain quickly, but that methamphetamine clears the brain later and affects more brain regions than cocaine. "This ... may help explain why the drug has such long-lasting behavioral and neurotoxic effects," lead author Joanna Fowler said.

The researchers also separated their subjects by race to see if there were any differences that might explain why rates of methamphetamine abuse are higher among African Americans than Caucasians. However, while the scientists found significant differences in rates of uptake of cocaine -- African Americans showed higher uptake, later rise to peak levels, and slower clearance -- the scientists failed to find similar differences in methamphetamine metabolism.

"The differences observed for cocaine pharmacokinetics are surprising considering there are no differences in cocaine abuse prevalence between these two ethnic groups," Fowler noted.

The findings will be published in the Nov. 1, 2008 issue of the journal NeuroImage.