A new study suggests that amphetamines have a more pronounced effect on men's brains and triggers the release of three times as much of the feel-good brain chemical dopamine than in women.
Researchers say the results may help explain why a greater number of men abuse amphetamines than women and may lead to more effective drug addiction treatments.
Sex Influences Amphetamine Response
In the study, scheduled for publication in the July issue of Biological Psychiatry, researchers compared the effects of amphetamines on dopamine release in the brains of 28 men and 15 women. Dopamine is part of brain's pleasure and reward system and has been linked to drug addiction.
Researchers injected amphetamines into the study participants. Brain scans showed that even though men and women had an equal number of dopamine receptors, exposure to amphetamine caused a much bigger surge in dopamine levels in men than in women.
The participants were also asked to rate their responses to the drug, including positive effects such as high, rush, liking, and desire for the drug as well as negative effects such as fidgetiness, anxiety, dizziness, dry mouth, and distrust.
The results showed that men's subjective responses to amphetamine were significantly higher than women's in all categories except dizziness.
The participants signed consent forms to be injected with amphetamines. During the study, they had continuous heart monitoring.
Men May Be Prone to Amphetamine Abuse
"These appear to be the first clinical studies whose results may help explain why we see a greater number of men abusing amphetamines than women," says researcher Gary S. Wand, MD, professor of endocrinology at Johns Hopkins School of Medicine in Baltimore, in a news release. "The fact that the subjective tests supported the biological ones further supports the hypothesis that men exhibit a higher response to amphetamines than women."
Researchers say 6% of American men compared with 3.8% of women aged 12 and older illegally used amphetamines in 2004. They also note that is not clear how difference in sex is related to difference in the dopamine response, but sex hormones may be involved.