Snake-oil salesmen used to prey on women with their "medicinal" tonics packing 40-proof alcohol. Mick Jagger sang of "mother's little helper."

A woman's addiction to alcohol, pills and other drugs has long been a wink-wink topic — one that garners a few smirks, rarely taken seriously.

The focus has always been on men, who traditionally have had higher rates of substance abuse.

But now the gender gap is closing. More than 20 million girls and women in the United States abuse drugs and alcohol, and 30 million more are addicted to cigarettes, according to a 10-year research effort from the National Center on Addiction and Substance Abuse (CASA) at Columbia University.

The study documents how women, pound for pound, not only get drunk or high faster then men, but also become addicted more easily.

The research results are presented in a new book from CASA called "Women Under the Influence" (Johns Hopkins University Press, 2006).

Double shot

The numbers could get worse, warns Susan Foster, CASA's director of policy research and analysis, who directed the research behind the book.

Teenage girls now smoke, drink and abuse drugs as often as teenage boys. For certain drugs, such as prescription painkillers, the abuse rate is higher in girls than boys.

Yet even as the rate of abuse becomes equal, physiological and psychological factors combine to ensure that females are more greatly affected by drugs and alcohol.

According to Foster, each single drink hits a woman like a double.

A woman's body contains less water and more fatty tissue — which increases alcohol absorption — compared to a male body. And women have a lower activity level of an enzyme called alcohol dehydrogenase (ADH), which breaks down alcohol.

Similar biological factors are at work in metabolizing illicit drugs.

Hooked on less

The risk of addiction to alcohol and drugs, including nicotine, is approximately doubled as well. The reason may be hormonal or psychological, according to ongoing research at the National Institute on Drug Abuse.

Males and females abuse drugs for different reasons. For example, teenage girls are more likely than boys to abuse substances in order to lose weight, relieve stress or boredom, improve their mood, reduce sexual inhibitions, self-medicate depression and increase confidence, according to CASA.

"Whereas the substance-abuse field has a fairly good understanding of the biological basis of gender differences in susceptibility to alcohol addiction, the research on such differences with regard to narcotic addiction is still in the early stages," Foster told LiveScience. "Women become addicted [to narcotics] faster than men. Our understanding of why this may be the case is more limited."

Foster is calling for more research funding for this neglected area. Similarly, CASA president Joseph Califano said that drug-treatment programs have long had a male-dominated, one-size-fits-all focus and need to better embrace women and their needs.

More than 90 percent of American women in need of treatment don't get it, said Califano, who served as United States Secretary of Health, Education and Welfare under President Jimmy Carter.

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