Once, most medical research was carried out only on men and male lab animals. That wall began to crack when Marilyn Carroll’s graduate student Wendy Lynch announced that there was no justification for excluding females, and she was going to study differences in drug addiction between the sexes. Lynch and Carroll, a professor in the Departments of Psychiatry and Neuroscience, began studies that opened the world’s eyes to the different addiction landscapes that men and women tread.
In 2000 Carroll’s group was the first to report differences in addiction liability. For example, estrogen prolonged drug-seeking—in females more than males—but progesterone, a hormone released after each ovulation and in pregnancy, reduced females’ drug-seeking to the level of males.
“This holds across cocaine, nicotine, opioids, and other drugs,” Carroll notes.
Combining progesterone with atomoxetine—a drug that reduces impulsive behavior—or with exercise worked even better to suppress both the seeking and the taking of cocaine. This work has led to precision treatments that have specific effects in men vs. women.
“Initial results suggest that they work better in females compared to males to reduce stimulant-seeking behavior,” Carroll says.
Carroll and Sharon Allen, a professor in the Department of Family Medicine and Community Health, are now studying progesterone as a treatment for addiction to nicotine, cocaine, and heroin.
As a result of Carroll’s and others’ work, in 2016 the National Institutes of Health ruled that both sexes must be studied in all investigations where there is no compelling scientific reason not to.
Carroll and colleagues have also found that individual predispositions can predict the severity of addiction. Predispositions associated with greater severity include craving for sweets, novelty-seeking behavior, and a tendency to act impulsively. Treatments based on this work are in development.
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