Drug injection is a method of introducing a drug into the bloodstream via a hollow hypodermic needle and a syringe, which is pierced through the skin into the body (usually intravenously, but also at an intramuscular or subcutaneous location). As of 2004 , there were 13.2 million people worldwide who used injection drugs, of which 22% are from developed countries.
A wide variety of drugs are injected, often opioids: these may include legally prescribed medicines and medication such as morphine, as well as stronger compounds often favored in recreational drug use, which are often illegal. Although there are various methods of taking drugs, injection is favoured by some people as the full effects of the drug are experienced very quickly, typically in five to ten seconds. It also bypasses first-pass metabolism in the liver, resulting in higher bioavailability and efficiency for many drugs (such as morphine or diacetylmorphine/heroin; roughly two-thirds of which is destroyed in the liver when consumed orally) than oral ingestion would. The effect is that the person gets a stronger (yet shorter-acting) effect from the same amount of the drug. Drug injection is therefore often related to substance dependence.
In recreational-use drug culture, preparation may include mixing the powdered drug with water to create an aqueous solution, and then the solution is injected. This act is often colloquially referred to as "slamming", "shooting [up]", “smashing”, "banging", "pinning", or "jacking-up", often depending on the specific drug subculture in which the term is used (i.e. heroin, cocaine, or methamphetamine).
In addition to general problems associated with any IV drug administration (see risks of IV therapy), there are some specific problems associated with the injection of drugs by non-professionals, such as:
- Chance of infection — This is generally a twofold major concern:
- Increased chance of overdose — Because IV injection delivers a dose of drug straight into the bloodstream, it is harder to gauge how much to use (as opposed to smoking or snorting, where the dose can be increased relatively incrementally until the desired effect is achieved; this gives a user who is in danger of overdosing a chance to seek medical treatment before respiratory arrest sets in). In addition, because of the rapid onset of intravenous drugs, overdose can occur very quickly, requiring immediate action. Another reason that overdose is a risk is because the purity of street drugs varies a great deal.
- Scarring of the peripheral veins — This arises from the use of blunt injecting equipment. This is particularly common with users who have been injecting while in jail and re-use disposable syringes sometimes hundreds of times. IV drug use for an extended period may result in collapsed veins. Though rotating sites and allowing time to heal before reuse may decrease the likelihood of this occurring, collapse of peripheral veins may still occur with prolonged IV drug use. IV drug users are among the most difficult patient populations to obtain blood-specimens from because of peripheral venous scarring. The darkening of the veins due to scarring and toxin buildup produce tracks along the length of the veins and are known as track marks.
- Arterial damage — Arterial pseudoaneurysms may form at injection sites, which can rupture, potentially resulting in hemorrhage, distal ischemia, and gangrene. Inadvertent intra-arterial injection can also result in endarteritis and thrombosis, with ultimately similar consequences.
- Increased chance of addiction — The heightened effect of administering drugs intravenously can make the chances of addiction more likely.
- Social stigma — In many societies, there is a social stigma attached to IV drug use, in addition to the more general stigma around illegal drug use and addiction.