Injection Drug Use

Updated: Apr 19, 2022
  • Author: Hammad Khan, MD, MPH; Chief Editor: Glen L Xiong, MD  more...
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With recent UN reports estimating that as many as 14.2 million individuals inject substances worldwide, injectable drug use continues to be a growing global concern given the increased risk for various health-related consequences faced by these individuals. [1]

Although most persons who inject drugs (PWID) do so by injecting their drugs intravenously, subcutaneous injection (ie, "skin-popping") is also common, as is intramuscular injection, which may occur intentionally or when an individual misses the vein or the subcutaneous space. Injecting drug use is associated with many local and systemic complications as well as with the transmission of infectious diseases via needle sharing and/or sexual activity. The most commonly injected drug is heroin, but amphetamines, buprenorphine, benzodiazepines, barbiturates, cocaine, and methamphetamine also are injected. Treatment of PWID may be complicated by social and political barriers to treatment and by a lack of resources for public health approaches to treatment.

Both illegal drug production and injecting drug use have been globalized in recent years. Although three countries – the United States, Russia, and China – continue to account for nearly half of all individuals who inject drugs, populations of PWID have increased worldwide; notably, the introduction of and rapid increase in injecting drug use is associated with dramatic increases in HIV infection in some areas. In China, Central Asia, and in several Eastern European countries, injection drug use is the primary risk factor for HIV infection. Further, there is concern that stressors related to the global COVID-19 pandemic may further exacerbate this public health issue.



When injecting a drug intravenously, the individual introduces a bolus of this substance into the vein, producing a rapid and powerful drug high. The onset of drug effects is about 15–30 seconds for the intravenous route and 3–5 minutes for the intramuscular or subcutaneous route. Drug effects from inhaling (ie, smoking) a substance can begin in 7–10 seconds and drug effects from intranasal use (ie, transmucosal absorption) can begin in 3–5 minutes.

Injected substance use causes many medical problems by introducing pathogens and other contaminants into the body via shared needles, a lack of sterile preparation, and poor injection techniques. Medical problems also arise from damage caused by the substances themselves (eg, morbidity and mortality associated with drug overdose). The injected drugs also may not be pure; they may be cut with irritants, such as talc, lactate, or quinine.

The injected substance is also associated with life-threatening or lethal outcomes. Death from the direct toxic effects of a heroin overdose itself is usually associated with respiratory depression, coma, and pulmonary edema. Death from the direct effects of cocaine is often associated with cardiac dysrhythmias and conduction disturbances, leading to myocardial infarction, stroke, and possible sudden death.




According to the 2021 World Drug Report of the United Nations Office on Drugs and Crime (UNODC), 269 million people used an illicit drug in 2018. By the year 2030, this number is expected to increase to 299 million people – an 11% increase. 

The joint UNODC/WHO/UNAIDS/World Bank estimate for the number of people who injected drugs (PWID) worldwide in 2019 is 11.2 million (range: 8.9 million to 14.2 million), corresponding to 0.22% (range: 0.18 to 0.28%) of the population aged 15–64 years. Injecting drug use remains highly prevalent in Eastern Europe, Central Asia and Transcaucasia and North America, with rates that are 5.7, 2.8, and 2.5 times the global average, respectively. In terms of the number of PWID worldwide, most of them reside in East and South-East Asia (27%), North America (16%), and Eastern Europe (15%). [1]

Among people ages 12 years and older in 2019, 57.2 million people used illicit drugs in the past year, according to the National Survey on Drug Use and Health (NSDUH). Among people ages 12 years and older, the percentage who used illicit drugs in the past year increased from 17.8% (or 47.7 million people) in 2015 to 20.8% (or 57.2 million people) in 2019. [2]

In the United States, the Center for Disease Control (CDC) noted an increase in substance use and drug overdose deaths during the COVID-19 pandemic. Between June 2020 and June 2021, the number of drug overdose deaths in the United States increased by nearly 19%. There is also concern that the number of PWID has presumably also grown during the pandemic and may continue to grow due to the mental health impacts of the pandemic. [3]


Morbidity and mortality may result from a wide range of factors including but not limited to: infection secondary to injecting drug use, sequelae of injection with adulterants added to the drug mixture, sequelae of the drug use itself, drug overdose, or violence associated with drug use.

  • According to the CDC, about 1 in 10 new HIV diagnoses in the United States are attributed to injection drug use or male-to-male sexual contact after injection drug use. Adult and adolescent PWID accounted for 10% (3,864) of the 37,968 new HIV diagnoses in the United States  and dependent areas in 2018 (2,492 cases were attributed to injection drug use and 1,372 to male-to-male sexual contactd and injection drug use). [4]  Of the 3,864 PWID newly diagnosed with HIV, most were men.

  • Another significant source of HIV infection for women is sex with partners who use injection drugs. An estimated 61% of AIDS cases in women can be attributed to injecting drug use or to sex with partners who use injection drugs. Females may use more shared injecting drug use equipment than males. [5]

  • Besides direct transmission of HIV, injecting drug use also contributes to the spread of HIV infection by perinatal transmission and by sexual contact with individuals who do not inject drugs. [6] Injecting drug use is also associated with increased levels of high-risk sexual behavior.

  • Worldwide, 40–60% of individuals who use injection drugs are estimated to be positive for hepatitis B, and 60–70% are positive for hepatitis C virus (HCV). HCV rates are high even in countries with low HIV seroprevalence. Injecting drug use is responsible for approximately 60% of HCV infections in the United States. New HCV infections in the United States have declined since 1989, [7]  but the incidence and prevalence of HCV remains high. The spread of HCV is rapid among those who are new to injecting drugs; in the United States, following initiation of injecting drug use, 50–80% become infected with HCV within 6–12 months. Reductions in risky injection-related practices among young users may improve both the burden of chronic HCV infection-related liver disease and elevated viral load-related poor treatment response. [8] Another option for reducing HCV transmission is encouraging users to use intranasal drugs as an alternative to injection drugs. [9] For related information, see Medscape's Hepatitis B and Hepatitis C Resource Centers.

  • The mortality from all causes in individuals who use injection drugs is estimated to be 3–4% per year.


Worldwide, 70–90% of those who use injection drugs are believed to be male.

The purity of heroin has been increasing, and its cost has been decreasing. Because of these factors and because of their initial desire to avoid injecting drug use, many adolescents and young adults in the United States and Europe using heroin for the first time try snorting, sniffing, or smoking heroin. New noninjecting heroin users have been known to make a transition to injecting drug use when their need for heroin use intensifies.

Among adolescents who inject drugs, early school truancy and expulsion may be a predictor of increased injecting drug use. A younger age of initiation into injecting drug use is associated with more frequent reports of risky drug use and sexual practices, as well as higher rates of HIV infection. [10]


Patient Education

Chemical dependency treatment provides education and skills training regarding abstinence from drug use. For those individuals who are not yet able to abstain from injecting drug use, harm reduction approaches are used to educate about methods of safer injection, including the use of clean needles, sterile injection techniques, and safe disposal of needles. [11]  Such outreach approaches are effective in promoting behavior change and slowing the spread of HIV and other infections. [12, 13]

Informal needle exchange programs in the United States began as early as the 1970s. In 1988, the New York City Health Department began the first government-sponsored needle exchange program in the United States. Usually, needle exchange programs operate by exchanging the used needles for an equal number of clean needles and syringes. Needle exchange programs may make referrals for chemical dependency treatment and medical treatment and may participate in other public health initiatives, such as distributing condoms and arranging HIV testing.

In some areas, needles and syringes are available for purchase from a pharmacy without a prescription. Those who purchase needles and syringes from pharmacies are less likely to participate in high-risk activities, such as using the services of crack houses or shooting galleries.

Several countries have developed harm reduction programs with different methods, including the introduction of syringe vending machines [14]  and safe injecting areas or rooms.

Programs that distribute injectable naloxone to individuals for use in suspected overdose situations have been implemented in many larger US cities.

To reduce risks associated with injecting drug use, clinicians and public health workers must raise awareness of the health consequences and risks of injection, make contact with the target population by improving access and outreach, provide the means to change risky behavior, and gain political and community support for the measures introduced.