Throughout the history of modern medicine, substance-abuse researchers have focused their investigations almost exclusively on men. It wasn't until the 1990s that scientists, prompted by federal funding aimed at enrolling more women in studies, began widely exploring how drug dependence and abuse affects women.

And it turns out that gender differences can be profound.

Women tend to become dependent on drugs more quickly than men, according to the most recent data from the Substance Abuse Mental-Health Services Administration. This is especially the case among those who abuse alcohol, marijuana, and opioids like heroin. Women also find it harder to quit and can be more susceptible than men to relapse, according to Harvard Medical School.

Heroin use has increased dramatically in the United States in the past decade. A new report from the Centers for Disease Control finds heroin use has increased across all income levels and in most age groups.

About 9 percent of those surveyed said heroin would be “fairly or very easily available,” according to the most recent Health and Human Services data. Three in 1,000 Americans report having used heroin in 2013, the most recent year for which data is available. That’s up from two in 1,000 people who reported using heroin a decade ago, according to the Associated Press, and represents 300,000 more heroin users in a span of 10 years. Heroin use among women doubled in that time.

“We have seen increases in groups such as women, non-Hispanic whites, higher incomes, and the privately insured,” said Eric Pahon, a spokesman for the Food and Drug Administration. “These new demographic groups closely resemble the populations with high rates of prescription opioid abuse in the past 15 years.”

In many cases, people are thought to be turning to heroin as a cheaper alternative to prescription pain pills. Nearly half of people who reported using heroin were also addicted to opioid painkillers, the CDC reported.

“We also know that the supply of heroin in the United States has increased substantially in the last few years and law enforcement reports indicate that heroin is showing up in communities where it has not typically been found,” Pahon told me. “These demographic shifts highlight the importance of reaching physicians with messages about appropriate prescribing of opioids, identifying people with problematic use as early as possible.”

Women face other risks associated with heroin. They're far more likely than men to be introduced to heroin injection by a sexual partner, and women report feeling more influenced by social pressure as a result, according to a 2010 study by the National Institutes of Health. “Research to understand gender differences in heroin abuse is certainly important because it could identify different patterns of use as well as different responses to treatment modalities or how treatment is provided,” said Christopher M. Jones, a senior health strategist at the FDA in an email. “I think there is a need for more research on gender differences for substance abuse generally.”

One key difference between men and women heroin users: Women often take heroin in smaller doses than men do, which may explain why men are more likely to die from overdoses. The number of overdose deaths involving heroin was nearly four times higher for men than it was for women in 2013, according to the CDC.

But with increased use among women, that may change. Since 2002, heroin deaths in the United States have quadrupled.