Nearly everyone ends up experimenting with an addictive substance — be it alcohol, nicotine or illicit drugs — at some point.
So why then, do some become dependent while others can enjoy the occasional martini, cup of coffee, or cigarette? Accumulating research suggests that the answer may be different for men than it is for women.
Long considered a man's problem, substance abuse related illnesses are responsible for the deaths of 200,000 American women annually and more than 4 million women are in need of treatment for their addiction.
Emerging evidence suggests that there are distinct male and female patterns of addictive disorders. Studies show men and women differ in their motivations to use, susceptibility to addiction, and response to pharmacological and psychological treatment.
Findings presented at the recent annual meeting of the Society for Neuroscience add to mounting evidence suggesting estrogen plays a role in sex-based addiction differences.
Virtually all addictive substances cause brain cells to release a chemical called dopamine. Dopamine is a feel-good compound that evolved to reinforce essential behaviors like mating and eating. Thus, when a person uses a drug, the consequent dopamine burst motivates them to want to recreate what the body views as "essential behavior" again and again.
More than a decade of research in humans and laboratory animals suggests that estrogen influences the amount of dopamine released in response to sexual activity and addictive drugs. Studies also show that a woman's reaction to stimulants like amphetamine and cocaine varies with her menstrual cycle.
These and other sex differences prompted Jill Becker and colleagues at the University of Michigan to further investigate the role of estrogen in cocaine addiction. Data show women become dependent after using cocaine for shorter amounts of time in smaller doses compared with men.
Motivation to use cocaine, both initially and in relapse from drug abuse treatment, also seems to vary by gender. Studies reveal that women tend to use cocaine to self-medicate when feeling depressed and unhappy. Men, on the other hand, generally use cocaine when they are feeling good, in order to feel even better.
Becker studied the influence of estrogen on "sensitization" to cocaine in rats. Sensitization, an integral part of addiction, refers to long-term changes that occur in the brain in response to using addictive substances.
Symptoms of cocaine sensitization in humans include rapid talking, compulsively moving around, and repetitive mouth movements. In rats, head bobbing, chewing, forelimb movement and turning in circles signal sensitization to cocaine.
After three weeks of use, all animals became sensitized to cocaine. Female rats who received estrogen plus cocaine, however, showed 20 percent to 50 percent more sensitization than either female rats who did not receive estrogen or males. Two weeks after receiving estrogen, female rats continued to exhibit greater behavioral responses to cocaine than those who did not receive estrogen.
According to Becker, these results suggest estrogen affects the immediate response to cocaine, as well as the long-term changes that occur in the brain as a result of drug use.