Heroin is used through four main routes: intravenous injection, smoking (inhaling heated vapor), snorting (intranasal insufflation), and intramuscular or subcutaneous injection. Each method delivers the drug at a different speed and intensity, and each carries its own set of health risks beyond the dangers of the opioid itself. Injection remains the route most closely linked to overdose and infectious disease, but non-injection routes carry serious hazards that users sometimes underestimate.
Intravenous Injection
Injecting heroin directly into a vein is the fastest way to feel its effects. After an IV dose, heroin reaches peak concentrations in the bloodstream almost immediately and then disappears from the blood with a half-life of only about three to four minutes as it is rapidly converted into active metabolites that cross into the brain.1Translational Psychiatry. Heroin and its metabolites: relevance to heroin use disorder This speed is what produces the intense “rush” that IV users describe. It is also what makes injection the most dangerous route for overdose: a large quantity of heroin floods the bloodstream before the user has any opportunity to gauge the dose. In a study comparing routes of administration, injecting heroin immediately before an overdose carried roughly 16 times the risk of overdose compared to using other routes, with the risk even higher among people who did not use heroin daily.2PubMed. Factors associated with non-fatal heroin overdose: assessing the effect of frequency and route of heroin administration
IV injection also exposes users to a cascade of vascular problems over time. Repeated needle punctures damage the walls of veins, leading to a condition called venous sclerosis, where veins harden and collapse. Once accessible arm veins are destroyed, people often move to riskier injection sites, including the femoral vein in the groin or even the jugular vein in the neck.3PubMed Central. Fire in the vein: Heroin acidity and its proximal effect on users’ health Injecting into the femoral vein is strongly associated with deep vein thrombosis, blood clots that can travel to the lungs and become life-threatening.4PubMed. Associations between injecting illicit drugs into the femoral vein and deep vein thrombosis: A case control study
Intramuscular and Subcutaneous Injection
Not every injection goes into a vein. Some users inject heroin into muscle tissue (“muscling”) or just under the skin (“skin popping”), either deliberately or because they cannot find a usable vein. The experience is noticeably different from IV use. Heroin injected into muscle is released slowly into the bloodstream, with a half-life roughly double that of an IV dose, producing a calmer and more prolonged high rather than the sharp rush of an IV shot.1Translational Psychiatry. Heroin and its metabolites: relevance to heroin use disorder A pharmacokinetic study found that intramuscular dosing resulted in sustained heroin exposure and delayed peak concentrations of its metabolites compared with intravenous dosing.5PubMed. Pharmacokinetics of high doses of intramuscular and oral heroin in narcotic addicts
The trade-off is a substantially higher risk of skin and soft-tissue infections. Subcutaneous or intramuscular injection is a major risk factor for abscesses, which are painful pockets of pus that often require surgical drainage and hospitalization.6Clinical Infectious Diseases. Risk Factors for Skin and Soft-Tissue Abscesses among Injection Drug Users: A Case-Control Study The drug pools in tissue rather than dispersing through the bloodstream, creating an environment where bacteria thrive. For people who have lost venous access and are forced into subcutaneous injection, abscesses can become a recurring problem.
Snorting
Snorting heroin involves inhaling the powder through the nose, where it absorbs through the mucous membranes. Peak blood levels appear within about five minutes, a timeline similar to intramuscular injection, though the potency is estimated to be roughly half that of an intramuscular dose.7PubMed. Pharmacokinetics and pharmacodynamics of intranasal “snorted” heroin The onset is slower and less intense than injection, which is one reason snorting is often a person’s first method of heroin use. Many people perceive it as safer, and by some measures it is: blood concentrations tend to be lower, and the slower absorption gives the body more time to respond.
That perceived safety has limits. An analysis of fatal heroin overdoses found that people who died after snorting or smoking heroin had significantly lower blood morphine levels than injectors, but they were still dead. The variability in blood concentrations was high, and a major contributing factor in these deaths appeared to be reduced tolerance after periods of abstinence, when users returned to a dose their body could no longer handle.8PubMed. Fatal intoxication as a consequence of intranasal administration (snorting) or pulmonary inhalation (smoking) of heroin
Chronic snorting also causes direct damage to the nose and throat. A case series documented a range of complications among habitual heroin snorters, including nasal perforation, nasal septum necrosis, pharyngeal ulceration, and damage to the palate.9PubMed. Necrosis of the intranasal structures and soft palate as a result of heroin snorting: a case series These injuries result from the corrosive effects of heroin and its adulterants on delicate tissue, compounded by reduced blood supply from chronic irritation.
Smoking and Inhaling Heroin Vapor
Smoking heroin, sometimes called “chasing the dragon,” involves heating heroin on foil and inhaling the vapor through a tube. It is one of the faster routes: heroin appears in the blood within a minute or two after smoking, peaking within one to five minutes, which is roughly comparable to the speed of IV injection.10Journal of analytical toxicology. Pharmacokinetics and pharmacodynamics of smoked heroin However, the bioavailability is highly variable because much of the drug is lost to the air, destroyed by heat, or left as residue on the foil. This means users get an unpredictable fraction of what they intend to consume.
The most alarming risk specific to smoking heroin is a rare but devastating neurological condition known as heroin inhalational leukoencephalopathy, or “chasing the dragon syndrome.” It involves progressive damage to the brain’s white matter, causing symptoms ranging from unsteadiness and slurred speech to a fully incapacitated, unresponsive state.11PubMed Central. Chasing the Dragon Syndrome: A Case of Toxic Leukoencephalopathy and Response to Intravenous Immunoglobulin Brain imaging in affected patients shows a distinctive pattern of symmetrical abnormalities in the white matter of the cerebellum and other deep brain structures.12PubMed. Neuroimaging features of heroin inhalation toxicity: “chasing the dragon” There is no established treatment, and some patients progress rapidly from mild coordination problems to a state requiring full-time care. Research on a small number of patients showed elevated lactate in the brain’s white matter, suggesting that the toxic product of heated heroin disrupts the energy-producing machinery inside cells.13PubMed. Leukoencephalopathy and raised brain lactate from heroin vapor inhalation (“chasing the dragon”)
Long-term heroin smoking also damages the lungs. A study of chronic heroin smokers found that a majority had advanced chronic obstructive pulmonary disease (COPD), with emphysema being the most common comorbidity at 27%, and roughly 15% suffering from frequent respiratory failure.14PubMed Central. The Association between Chronic Heroin Smoking and Chronic Obstructive Pulmonary Disease These lung effects build up over years of exposure and can be irreversible.
Oral Use
Swallowing heroin is uncommon because the body’s first-pass metabolism rapidly converts it into morphine before it ever reaches the brain, stripping away the intense rush that users seek. Still, oral heroin does produce pharmacological effects, and its behavior is more complicated than you might expect. A study comparing oral heroin to oral morphine found that heroin actually produced a higher peak morphine concentration in the blood than an equivalent dose of morphine itself, with bioavailability climbing substantially at higher doses and in people with chronic opioid exposure.15PubMed Central. Oral diacetylmorphine (heroin) yields greater morphine bioavailability than oral morphine: bioavailability related to dosage and prior opioid exposure In other words, swallowing heroin is not simply the same as swallowing morphine. But the slower, less euphoric experience makes this route unappealing to most people seeking heroin’s characteristic effects, which is why it remains a niche method mostly encountered in supervised medical settings in a handful of countries.
Blood-Borne Infections and Shared Equipment
Injection, by any route, creates a direct pathway for pathogens to enter the bloodstream. Hepatitis C (HCV) and HIV are the most well-known risks, and transmission does not require sharing needles. Sharing any part of the injection kit increases the danger. A study of people who injected drugs found that even among those who never shared needles, sharing cookers and cotton filters was associated with nearly six times the risk of HCV infection, and over half of HCV infections in non-syringe-sharers were attributable to sharing those items alone.16PubMed Central. Sharing of drug preparation equipment as a risk factor for hepatitis C Another study confirmed that sharing containers and filters carried around three times the odds of recent HCV infection, independent of needle sharing.17PubMed. Risk of transmission associated with sharing drug injecting paraphernalia: analysis of recent hepatitis C virus (HCV) infection using cross-sectional survey data
The contamination pathways are deeply embedded in how heroin is prepared in group settings. In a survey of heroin-injecting networks, 86% of networks reported using a common cooker, 82% reported dividing the drug as a liquid, and 67% reported using a shared water reservoir that syringes had been rinsed in. Only 22% reported sharing syringes directly, meaning the focus on needle sharing alone misses the majority of transmission risk.18PubMed. Drug sharing among heroin networks: implications for HIV and hepatitis B and C prevention
Injection drug use is also a rising cause of infective endocarditis, a serious infection of the heart valves. The American Heart Association issued a scientific statement specifically addressing the increasing incidence of endocarditis among people who inject drugs.19PubMed. Management of Infective Endocarditis in People Who Inject Drugs: A Scientific Statement From the American Heart Association Endocarditis in this population can involve multiple organisms simultaneously and lead to complications throughout the body, including septic emboli to the lungs, splenic infarction, and kidney damage.20PubMed Central. Polymicrobial endocarditis in intravenous heroin and fentanyl abuse
Cotton Fever and Other Injection-Specific Reactions
People who inject heroin commonly filter their dissolved drug through small pieces of cotton to remove particles before drawing it into a syringe. This practice can cause a distinctive short-lived illness known as “cotton fever,” characterized by high fever, muscle aches, nausea, and vomiting that typically appear within minutes of injection and resolve within hours.21PubMed Central. Cotton Fever: Does the Patient Know Best? The leading explanation is that a bacterium commonly found on raw cotton releases a toxin that triggers the body’s inflammatory response when injected into the bloodstream.22PubMed Central. Just a Bad Case of Cotton Fever: A Case Report and Literature Review While cotton fever itself is usually self-limiting, it creates a diagnostic headache in emergency rooms because its symptoms overlap with early sepsis and endocarditis, both of which require immediate treatment.
The acidity of heroin solutions also causes direct vascular harm. Heroin base (common in parts of Europe) does not dissolve in water on its own, so users add citric or ascorbic acid. If too much acid is added, the resulting low-pH solution damages vein walls on injection and can cause the heroin to precipitate out of solution inside the vein, compounding the injury.23PubMed Central. A method of diamorphine (heroin) administration for harm reduction This kind of chemical damage accelerates the loss of usable veins that pushes long-term injectors toward riskier sites.
How Heroin Formulation Shapes the Route
Heroin is not a single product. It exists in different chemical forms depending on where and how it was manufactured, and this directly affects which routes of administration are practical. Heroin hydrochloride, the salt form, dissolves readily in water and is well suited for injection or snorting. Heroin base, on the other hand, does not dissolve easily in water but vaporizes efficiently when heated on foil, making it the form typically used for smoking. The availability of these forms varies geographically. In the United Kingdom, for example, different forms of heroin with different origins have appeared on the black market at different times, with salt-form samples generally used by injectors and base-form samples used by people who chase the dragon.24PubMed. Potential risk factors for the transition to injecting among non-injecting heroin users: a comparison of former injectors and never injectors In parts of North America, heroin is more commonly sold as a powder that can be snorted or dissolved for injection, while “black tar” heroin, a crude form common in the western United States and Mexico, is typically dissolved with heat and injected or occasionally smoked.
This means that the heroin available to a person in a particular place often determines how they first use the drug, which in turn shapes their risk profile from the beginning.
The Shift from Non-Injection to Injection
Many people start using heroin through a non-injection route, then transition to injection over time. This pattern has been studied extensively because it represents a major escalation in health risk. Researchers have identified several factors associated with the transition: being homeless, being unemployed, starting heroin use at a younger age, having close social ties to people who inject, and having a partner who injects.24PubMed. Potential risk factors for the transition to injecting among non-injecting heroin users: a comparison of former injectors and never injectors Simply being around people who inject and seeing the act performed increases the perceived acceptability and the likelihood of being offered a syringe.25PubMed. Are non-injecting opioid users at risk of transition to injecting drug use? A multi-site study from India
The motivation for switching is often pharmacological: injection delivers more drug to the brain more quickly, meaning a person can get the same intensity of effect from less heroin, which matters when money is tight or tolerance has risen. Social environment research has framed the transition as partly driven by subcultural norms, where injection is modeled and reinforced within drug-using networks.26PubMed Central. Risk factors associated with the transition from heroin sniffing to heroin injection: a street addict role perspective Understanding these dynamics matters because the transition point is where many of the most severe health consequences begin: overdose risk jumps, infectious disease exposure climbs, and vein damage starts accumulating.
Adulterants That Change the Risk Equation
Street heroin is almost never pure. It is cut with inert fillers to increase weight and often adulterated with pharmacologically active substances that introduce hazards unrelated to the opioid itself. Two adulterants deserve particular attention because of their growing prevalence and serious consequences.
Fentanyl, a synthetic opioid roughly 30 to 50 times more potent than heroin, has become a widespread contaminant in the heroin supply, particularly in eastern North America. In Massachusetts alone, over 75% of more than 1,300 opioid-related deaths in one period tested positive for fentanyl.27PubMed. Xylazine Adulteration of the Heroin-Fentanyl Drug Supply: A Narrative Review Its presence makes every route of heroin use more dangerous because the user cannot gauge the actual potency of what they are consuming. A batch that looks and smells like ordinary heroin may contain enough fentanyl to be lethal. This is true whether the heroin is injected, snorted, or smoked.
Xylazine, a veterinary sedative that is not an opioid and does not respond to naloxone (the standard overdose-reversal drug), has been increasingly detected in the fentanyl-heroin supply.27PubMed. Xylazine Adulteration of the Heroin-Fentanyl Drug Supply: A Narrative Review It causes prolonged sedation and, in people who inject, is associated with severe necrotic skin wounds that resist healing. Levamisole, an antiparasitic drug used in veterinary medicine, has also been found in heroin and other street drugs since the early 2000s. It can trigger autoimmune reactions including dangerous drops in white blood cell counts, purpura (purple skin lesions from bleeding under the skin), and visible tissue death.28Therapeutic Drug Monitoring. Levamisole—a Toxic Adulterant in Illicit Drug Preparations: a Review These adulterant risks compound the hazards of whichever administration route a person uses.
Harm Reduction and Route-Switching Interventions
Public health programs have long focused on reducing the harms of injection through needle exchange, but some have also tried to encourage people to switch from injection to smoking, which avoids the risks of bloodborne virus transmission and vein damage. One evaluation of a program that distributed foil packs through needle exchange services found that 85% of participants reported using the foil to smoke heroin on occasions when they would otherwise have injected.29PubMed Central. Distributing foil from needle and syringe programmes (NSPs) to promote transitions from heroin injecting to chasing: an evaluation This kind of route-switching intervention does not eliminate the risks of heroin use, but it can reduce some of the most immediately dangerous ones, particularly when combined with naloxone distribution and access to treatment.
For people who continue injecting, harm reduction research has also examined better methods of dissolving heroin base to reduce acid-related vein damage. Current advice cards supplied with needle exchange kits instruct users to measure acid in “pinches,” which is inherently imprecise and can lead to solutions acidic enough to harm veins or cause the drug to precipitate out of solution inside the body.23PubMed Central. A method of diamorphine (heroin) administration for harm reduction These are narrow, unglamorous interventions, but for people already using heroin, they represent the difference between a manageable health risk and a catastrophic one.