O ver the last several years, there has been growing concern among the public and lawmakers in the United States about rising drug overdose deaths , many of which involved opioids. Congress has responded to the issue through legislative activity and funding, while the Administration has sought to reduce supply and demand of illicit drugs through enforcement, prevention, and treatment. This report does not provide a comprehensive overview of opioid abuse as a public health or criminal justice issue. Instead, it answers common questions that have arisen due to rising drug overdose deaths in the nation and the ensuing federal response. This section answers questions on the nature of opioid abuse in the United States. These questions provide background on the drugs that are abused, the associated harm to the population, and the extent of opioid abuse. An opioid is a type of drug that when ingested binds to opioid receptors in the body—many of which control a person's pain and other functions. While these drugs are widely used to alleviate pain, some are abused by being taken in a way other than prescribed (e.g., in greater quantity) or taken without a doctor's prescription. Many prescription pain medications, such as hydrocodone and fentanyl, are opioids, as is heroin (an entirely illicit drug). In its annual National Survey on Drug Use and Health (NSDUH), the Substance Abuse and Mental Health Services Administration (SAMHSA) does not collect data using the category "opioids"; rather, it collects data on use of heroin and misuse of prescription pain relievers. In 2016, SAMHSA estimated that 329,000 Americans age 12 and older were current users of heroin and approximately 3.8 million Americans were current "misusers" of prescription pain relievers. According to the same survey, an estimated 11.8 million people aged 12 and older misused opioids in the past year (i.e., the year preceding the date on which the individual responded to the survey) including 11.5 million misusers of pain relievers and 948,000 heroin users. In its annual survey of adolescent students, the Monitoring the Future Survey measures drug use behaviors among 8 th , 10 th , and 12 th graders. In 2016, 0.2% of surveyed adolescents were current users of heroin; 5.4% of surveyed 12 th graders were current users of "narcotics other than heroin." There are short-term and long-term effects of abusing opioids, but the most severe among them is the risk of overdose and death. Drug overdose deaths more than tripled from 1999 to 2014. In 2015, more than 52,000 people died from drug overdoses, and approximately 63% of those deaths involved an opioid. More than 15,000 overdose deaths involved prescription opioids, representing almost half of all opioid overdoses. Also, while U.S. life expectancy (at birth) increased by 2.0 years overall (due to decreasing death rates related to heart disease, cancer, etc.) from 2000 to 2015, researchers have found that the increase in opioid-related drug poisoning death rate reduced overall life expectancy by 0.2 years during this same time. Reports indicate that recent increases in overdose deaths are most likely driven by illicitly manufactured fentanyl and heroin. The National Institute on Drug Abuse (NIDA) states that fentanyl is largely to blame for the sharp increases in overdose deaths over the last several years. Further, NIDA explains that the number of fentanyl-related deaths is likely underestimated because some medical examiners do not test for fentanyl and some death certificates do not list specific drugs. Opioids are the primary drugs involved in drug overdose deaths. The number and rate of drug overdose deaths varies by region of the United States. As might be expected, given it is the most populous state in the country, California had the highest number of drug overdose deaths (4,659) in 2015; however, not all states with the highest number of overdose deaths correspond with their high rank in population size. For example, Ohio had the second highest number of overdose deaths (3,310) and Massachusetts had the 9 th highest number (1,724). These states rank 7 th and 15 th , respectively, in state population size. As shown in Figure 1 , age-adjusted overdose death rates tell a different story than unstandardized numbers of overdose deaths. The Northeast and Appalachian regions, as well as certain Southwest states, have higher rates of drug overdose deaths compared to the rest of the country. As mentioned, fentanyl may be largely to blame for the sharp increases in overdose deaths over the last several years. According to a NIDA-funded study, in 2015 New Hampshire had the most fentanyl overdoses per capita, and nearly two-thirds of the 439 drug overdose deaths in the state involved fentanyl. Heroin, fentanyl, and controlled prescription drugs have been ranked as the most significant drug threats to the United States. While the reported availability of controlled prescription drugs, which include opioids, has declined over the last several years, the reported availability of heroin has increased substantially. Further, there has been a rise in the availability of illicit fentanyl pressed into counterfeit prescription opioid pills. Opioids have been available in the United States since the 1800s, but the market for these drugs shifted significantly beginning in the 1990s. This section focuses on this latter period (see Figure 2 ) In the 1990s, the availability of prescription opioids, such as hydrocodone and oxycodone, increased as the legitimate production of these drugs and diversion of them increased sharply. This continued into the early 2000s, as abusers attained their prescription drugs through "doctor shopping," bad-acting physicians, pill mills, the Internet, pharmaceutical theft, prescription fraud, and family and friends. The federal government, along with state and local governments, undertook a range of approaches to reducing the unlawful prescription drug supply and prescription drug abuse, including diversion control through prescription drug monitoring programs, a crackdown on pill mills, the increased regulation of Internet pharmacies, the reformulation of OxyContin® (oxycodone hydrochloride controlled-release), and the rescheduling of hydrocodone. Some experts have highlighted the connection between the crackdown on the unlawful supply of prescription drugs and the subsequent rise in the heroin supply (as discussed in the next section) and abuse of the drug. Heroin is a cheaper alternative to prescription drugs that may be accessible to some who are seeking an opioid high. While most users of prescription drugs will not go on to use heroin, accessibility and price are central factors cited by patients with opioid dependence in their decision to turn to heroin. The trajectory of the heroin supply over the last several decades is much different than that of prescription opioids, but their stories are connected. In the late 1990s and early 2000s, white powder heroin produced in South America dominated the market east of the Mississippi River, and black tar and brown powder heroin produced in Mexico dominated the market west of the Mississippi. Most of the heroin destined for the United States at that time came from South America, while smaller percentages came from Mexico and Southwest Asia. Price and purity varied considerably by region. The average retail-level purity of South American heroin was around 46%, which was considerably higher than that of Mexican, Southeast Asian, or Southwest Asian heroin. At the time, Mexican heroin was around 27% pure, while Southeast Asian and Southwest Asian heroin were around 24% and 30% pure, respectively. Prices for heroin fell dramatically in the 1990s—it was 55% to 65% less expensive in 1999 than in 1989. Over the last several years, heroin prices have further declined, while purity, in particular that of Mexican heroin, has increased. The availability of Mexican heroin has also grown. Over 90% of the heroin currently seized in the United States is from Mexico (while a much smaller portion is from South America). Mexico dominates the U.S. heroin market because of its proximity and its established transportation and distribution infrastructure, which improves traffickers' ability to satisfy U.S. heroin demand. Increases in Mexican production have ensured a reliable supply of low-cost heroin, even as demand for the drug has increased. Mexican traffickers have particularly increased their production of white powder heroin and may be targeting those who abuse prescription opioids. Exacerbating the current opioid problem is the rise of non-pharmaceutical fentanyl on the black market. Diverted pharmaceutical fentanyl represents only a small portion of the fentanyl market. Non-pharmaceutical fentanyl largely comes from China, and it is often mixed with or sold as heroin. It is 50 to 100 times more potent than heroin, and over the last two years, reported prices ranged between $30,000 and $38,000 per kilogram. The increased potency of non-pharmaceutical fentanyl compounds, such as the recently emerged "gray death," is extremely dangerous. Law enforcement expects that the fentanyl market will continue to expand in the future as new fentanyl products attract additional users. The supply of opioids varies by region. In 2016, approximately 45% of respondents to the National Drug Threat Survey (NDTS) reported heroin as the greatest drug threat in their area. In contrast, 8% of respondents reported heroin as the greatest threat in 2007. Reports of heroin as the greatest threat are concentrated in the Northeast, Midwest, and Mid-Atlantic regions. Additionally, DEA investigative reporting indicates high controlled prescription drug availability in cities throughout the United States. Opioids are the main cause of drug overdose deaths. Reports indicate that increases in overdose deaths are most likely driven by illicitly manufactured fentanyl and heroin. The increasing availability of heroin throughout the United States largely, but not entirely, corresponds to high numbers of drug overdose deaths (see Figure 1 ).