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Reproductive hormones apparently cause men and women to react differently to cocaine, leading researchers to speculate that drug abuse treatment could be more effective if it were gender specific.

"The behavioral effects of cocaine do differ by sex," said Frans van Haaren, a University of Florida psychology research scientist. "We're also finding more and more evidence that reproductive hormones alter the effect of drugs in both acute and long-term use or abuse. This could have significant implications in the treatment of drug addiction."In studies on rats, van Haaren found that females and castrated males needed much smaller dosages of cocaine than non-castrated males to exhibit the same behavioral changes. This suggests that the level of testosterone alters the effects of cocaine, he said.

"We know that male and female subjects are different in a variety of respects, with one of the most important differences being the reproductive system and its associated hormones," van Haaren said. "It's long been assumed that the male system is stable since it has only one important hormone, but it very well may be that testosterone levels fluctuate as well."

Van Haaren, whose research is supported by a $330,000 grant from the National Institute on Drug Abuse, cited another study in which rats pressed levers to inject themselves with cocaine. Female rats spent much more time and effort to get the drug during certain phases of their hormonal cycle, he said.

"It appears that alcohol, marijuana and cocaine intake differ over the female cycle because hormones alter their effect," he said.

Another recently identified distinction between the sexes is that males naturally have more of the enzymes that break down alcohol in their system.

"Right now, males and females in drug or alcohol abuse centers are treated basically the same, even though there are generally more males in treatment," van Haaren said. "It could be that treatment and prevention would be more effective if it were to pay attention to the role of fluctuating reproductive hormone levels in the initiation and maintenance of drug abuse. This certainly is an important area of research and more should be done."

The difference in how the sexes react to alcohol and drugs has not been widely documented before because most drug trials were conducted exclusively on males until last year, when new federal regulations forced a change.

All-male test groups traditionally have been considered more efficient and reliable than female subjects, whose fluctuating hormones make research more difficult. For example, a highly publicized study several years ago found that people could reduce their chances of having a heart attack by taking aspirin on a regular basis, but the research was based on 22,000 men and no women.