A recent Vanderbilt University study showed that the hormonal cycles of women may not only make them more vulnerable to drug addiction, but also more affected by causes that contribute to relapse. The results are particularly important as there are almost no studies of dependence in women that account for these periods.

Erin Calipari, an assistant pharmacology professor at the Vanderbilt Center for Addiction Research, points out that women represent a particularly vulnerable population with higher addiction rates following drug exposure, but addiction studies focused primarily on the mechanisms underlying these effects in men. Her research found that women learn faster when the rates of fertility-related hormones are elevated, create stronger correlations of signals in their environment, and are more likely to seek rewards.

"Women becoming drug addicts may be a process fundamentally different from men," said Calipari. "It's important to understand this, because it's the first step in developing treatments that are actually effective." She said the next step would be to figure out specifics of how hormonal shifts affect the brains of women and, ultimately, develop medicines that might help override those. But even before these potential drugs were available, the data in this research could be used by treatment centers to educate women about their deeper psychological links to locations and objects. This can mean a higher risk of recurrence only by visiting, for instance, a place where they used medications or carrying the kind of spoon they used in the process.

Historically, scientists have specifically avoided using female animals in medical studies so they don't have to take into account hormone cycle effects. As a result, drug development has often centered on fixing men's dysfunctions, which may explain why women frequently fail to respond to available medications or therapies in the same way as men do, Calipari said.

Her work was recently published in Neuropsychopharmacology, a Nature-affiliated journal, in a paper entitled "Cues play a critical role in the estrous cycle-dependent enhancement of cocaine enhancement." In this study, male and female rats were allowed to dose themselves with cocaine by pushing a lever, with a light set up to be applied during dosing. This is similar to the environmental indications present when people take drugs, such as drug paraphernalia. If their circulating hormone levels were high, female rats made stronger correlations with the light and were more likely to continue to push the lever as much as possible to get any amount of cocaine.

Ultimately, in the presence of these signs, females were willing to "pay" more for cocaine. The findings can be applied to humans by behavioral economic analysis, which uses a complicated mathematical formula with the most and the least that a subject will do to get a payoff. It is one of the few ways it is possible to make correlations between ecosystems.

"We found the animals are only pressing a lever to get the light— that environmental stimuli," said Calipari. "That has meaning for them." There are epidemiological evidence it say women are more vulnerable, but the reasons are unknown. We know that they are transitioning to addiction faster and have more craving and relapse problems. Now, with studies like this, we are starting to separate environmental and physiological triggers. "This new research builds on earlier work conducted by Calipari at Mount Sinai's Icahn School of Medicine which showed estrogen intensifies the brain's cocaine dopamine reward.