How Does Smoking Heroin Affect the Brain and Lungs?

Smoking heroin involves heating the drug and inhaling its vapor, a practice that delivers the substance to the brain within minutes and produces effects comparable to intravenous injection. Often called “chasing the dragon,” the technique has spread across continents since it first appeared in the mid-twentieth century and remains one of the most common non-injection routes of heroin use worldwide. While many users perceive it as safer than injecting, smoking heroin carries its own serious and sometimes unique health risks, from severe lung disease to a rare but devastating form of brain damage.

Origins of “Chasing the Dragon”

The earliest form of heroin smoking appeared in Shanghai in the 1920s, where users heated the drug in porcelain bowls and inhaled the fumes through bamboo tubes. That method spread across Eastern Asia and eventually reached the United States over the following decade. A refinement emerged in or near Hong Kong in the 1950s: placing heroin on a strip of tin foil, heating it from below with a lighter or candle, and inhaling the rising vapor through a tube. The liquid heroin slides across the foil as it melts, leaving a dark trail that users follow with their inhaling tube. This pursuit of the moving droplet gave the practice its colloquial name.

From Hong Kong, chasing the dragon spread to other parts of Southeast Asia during the 1960s and 1970s, reached parts of Europe in the late 1970s and early 1980s, and moved through much of the Indian subcontinent during the 1980s.² In several European and Latin American cities, smoking gradually overtook injection as the dominant first route of heroin use, driven less by awareness of HIV risk than by shifting cultural norms and changes in heroin markets. In Seville, Spain, for instance, smoking became the only first route of administration reported by new users from 1991 onward.³

How Smoked Heroin Reaches the Brain

When heroin is heated on foil, it vaporizes and the user inhales the fumes into the lungs, where the drug crosses into the bloodstream through the thin walls of the air sacs. From there it reaches the brain rapidly. In pharmacokinetic studies, heroin appeared in the blood almost immediately after smoking and peaked within one to five minutes, a timeline similar to intravenous injection.⁴ That fast onset is part of what makes smoking heroin powerfully reinforcing: the user feels the rush almost as quickly as someone who injects.

The efficiency of the process, though, is lower. A substantial portion of the drug is lost to the air, destroyed by heat, or left as residue on the foil. Studies using pharmaceutically prepared heroin estimated that the bioavailability of inhaled heroin is roughly 52 to 53 percent, meaning only about half the dose actually enters the bloodstream.⁵⁶ Peak blood concentrations of heroin and its metabolites after inhalation are two to six times lower than after injection of the same dose. This lower efficiency means users tend to need more heroin to achieve the same effect, but it does not mean the route is safe.

The chemical form of heroin matters as well. Heroin base (the freebase form) vaporizes more efficiently than heroin hydrochloride (the salt form), and the various cutting agents mixed into street heroin can strongly influence how much active drug actually becomes airborne.⁷ This variability from batch to batch is one reason smoked heroin can be unpredictable in its effects.

Technique Matters More Than People Realize

Not all smoking methods deliver the same dose. A study comparing the classic chasing-the-dragon method to a commercially available heating device found that the heating device produced dramatically lower blood levels of heroin and its metabolites. Exposure to heroin was about 80 percent lower, and peak concentrations of both heroin and its first metabolite were 70 to 80 percent lower when the device was used instead of foil.⁸ In practical terms, someone switching between different smoking setups could experience very different levels of intoxication even with the same amount of heroin, which adds another layer of unpredictability.

Damage to the Lungs

The lungs take the first and heaviest hit from smoked heroin. Chronically inhaling heated heroin vapor leads to measurable, often severe, respiratory decline. In a study comparing heroin smokers to non-users, more than a quarter of heroin smokers had emphysema, and over half had advanced chronic obstructive pulmonary disease (COPD). At least 15 percent of the heroin smokers in that study experienced frequent respiratory failure.⁹ Their lung function scores were substantially lower than those of non-users, indicating that the airways were both narrowed and less able to move air.

What stands out in the research is how early this damage appears. Heroin smokers tend to develop emphysema at younger ages than would be expected from tobacco smoking alone.¹⁰ The mechanism is not entirely clear, but the combination of hot vapor, pyrolysis byproducts, and whatever adulterants are mixed into the supply creates a toxic cocktail for delicate lung tissue. Many heroin smokers also smoke tobacco or crack cocaine, which complicates the picture, but heroin inhalation appears to contribute independently to lung disease.

Asthma can also become acutely dangerous. Case reports describe patients with asthma who required mechanical ventilation shortly after inhaling heroin, with two of three patients in one series dying from acute severe asthma attacks.¹¹ For anyone with reactive airways, smoking heroin can trigger a life-threatening episode.

A Rare but Devastating Brain Injury

One of the most alarming consequences specific to smoked heroin is a condition known as heroin-associated leukoencephalopathy, sometimes called “chasing the dragon syndrome.” It involves progressive damage to the brain’s white matter, the insulation that coats nerve fibers and allows signals to travel efficiently. The condition was first identified in Amsterdam in 1982 and has been reported sporadically since.

In a clinical study of three heroin smokers, two who had inhaled heroin vapor daily over the course of two weeks developed increasingly severe neurological symptoms: problems with coordination, slurred speech, and difficulty walking. One patient deteriorated into an unresponsive state with rigid posturing and eventual paralysis of all four limbs. Brain scans showed widespread, symmetrical damage to white matter in the cerebellum, the back of the brain, and deep brain structures. A biopsy revealed spongy degeneration of the white matter, with tiny vacuoles forming within the myelin sheaths of nerve fibers.¹²

The exact cause remains debated. One hypothesis points to toxic pyrolysis products formed when heroin and its adulterants are heated, rather than the heroin itself.¹³ Because the condition has been reported in clusters tied to specific batches of street heroin, a particular contaminant or cutting agent may be involved. The rarity of the condition relative to the number of people who smoke heroin worldwide supports the idea that something beyond the drug itself triggers it. Regardless of the mechanism, the damage can be irreversible, and no reliable treatment exists once the syndrome progresses.

The Myth of a Safe Route

Many people begin smoking heroin specifically because they believe it is safer than injecting. That perception is understandable but incomplete. Smoking does avoid certain injection-specific risks: there is no needle to share, no risk of collapsed veins, and no direct introduction of bacteria into the bloodstream. But the assumption that smoking cannot cause a fatal overdose is dangerously wrong.

A forensic study of fatal heroin intoxications among people who smoked or snorted the drug found that while their blood morphine levels were significantly lower on average than those of injectors, the range of concentrations was enormous. Some non-injecting users who died had blood levels comparable to those seen in injection deaths. The researchers concluded that smoking heroin involves a reduced risk of reaching very high blood concentrations but still carries a considerable risk of lethal outcome, partly because of high variability from person to person and dose to dose.¹⁴ The study also highlighted a critical vulnerability: people who return to smoking heroin after a period of reduced use or abstinence may have lost their tolerance. They sometimes assume that because they are smoking rather than injecting, they can safely use at their previous dose. That miscalculation can be fatal.

Fentanyl Has Changed the Calculation

The infiltration of fentanyl and its analogs into the illicit opioid supply has reshaped the risk landscape for everyone who uses heroin, regardless of route. Fentanyl is far more potent by weight, and because it is often unevenly mixed into batches, a single dose from a contaminated supply can contain wildly variable amounts. People who reported exposure to fentanyl-contaminated heroin routinely experienced or encountered non-fatal overdoses.¹⁵

Research from California comparing people who smoked fentanyl to those who injected it found that injectors were about 40 percent more likely to have experienced a recent non-fatal overdose and roughly two and a half times more likely to have had a skin and soft-tissue infection.¹⁶ Smoking still came out as the less risky route by comparison, but the gap narrowed considerably in the fentanyl era. Even users who exclusively smoke fentanyl or fentanyl-contaminated heroin face overdose rates that would have been considered alarming a generation ago. The potency of the drug overwhelms some of the dose-buffering effect that the inhalation route previously provided.

Oral Health Deterioration

Heroin use, including smoking, takes a toll on oral health that often goes unnoticed until the damage is extensive. Opioids reduce saliva production, and saliva is one of the mouth’s primary defenses against tooth decay and gum disease. Without it, bacteria flourish. A study of former heroin users in a Chinese methadone treatment program found that nearly 65 percent had decayed or filled teeth, about 42 percent had residual roots from teeth that had broken down entirely, and over 99 percent showed gingival bleeding.¹⁷ The heat and chemical irritants from smoking compound the problem. Users who craved sugar while high and neglected dental care, which many did, experienced accelerated decay. Methadone treatment, while lifesaving for addiction, can further reduce saliva flow and worsen the cycle.

What Drives People to Smoke Rather Than Inject

Route choice is not purely individual. Research consistently finds that the social environment plays a powerful role. In a study of reasons for choosing an initial route of heroin administration, social pressure was the primary factor people cited for both starting to smoke and starting to inject. When people did resist the transition from smoking to injection, their resistance was typically rooted in direct observation of people who injected: seeing the physical deterioration, the abscesses, the difficulties with veins.¹⁸ Health concerns, especially fear of HIV and overdose, also deterred transition to injection, though having a sexual partner who injected was a strong predictor of eventually switching.¹⁹

These dynamics have practical implications for public health. In regions where heroin smoking norms are strong and injection is stigmatized within drug-using networks, fewer people transition to injecting, and the community avoids many injection-related harms. But when heroin markets shift, new populations enter drug use, or social networks change, the balance can tip quickly.

Effects During Pregnancy

Heroin use during pregnancy, by any route, carries serious risks for both mother and baby. Research has documented that heroin-exposed pregnancies are associated with fetal growth restriction, meaning babies are born significantly smaller than expected. Neonatal withdrawal syndrome, where the newborn experiences withdrawal symptoms after birth, is also common. Mothers face higher rates of placental abruption and sexually transmitted infections. However, studies have not found an increased rate of congenital birth defects in heroin-exposed infants compared to controls.²⁰ The smoking route does not eliminate any of these risks, because they are driven by the drug’s systemic effects rather than by the method of administration.

Harm Reduction and Supervised Inhalation

Recognizing that many people who use heroin prefer smoking and are unlikely to stop using entirely, some harm reduction programs have adapted. In Scotland, needle and syringe programs began distributing foil for heroin smoking. A study found that people who obtained foil from these services had much higher odds of smoking or snorting heroin rather than injecting. Those who smoked had lower odds of injecting multiple times daily and were less likely to inject into dangerous sites like the groin or neck.²¹ At the same time, smokers in that study had higher odds of having experienced a recent overdose, possibly because of the fentanyl-contaminated supply or because smoking attracted users with more chaotic use patterns.

Some cities have gone further. Supervised consumption sites in Canada began offering dedicated inhalation rooms, where people can smoke drugs under observation by trained staff who can intervene if an overdose occurs. These facilities have been heavily used since opening.²² A review of the broader literature on safer smoking programs found that when people who use drugs were provided with clean smoking equipment, they engaged in fewer risky behaviors such as sharing pipes or using broken equipment, and showed improved health outcomes.²³ These programs remain politically contentious in many jurisdictions, but the evidence increasingly supports their role in reducing preventable harm.

The Economic Weight of Heroin Use Disorder

The costs of heroin addiction ripple far beyond the individual user. In the United States, the total societal cost of heroin use disorder was estimated at $51.2 billion in 2015, averaging roughly $50,800 per person with heroin use disorder. The largest single expense was the cost of the heroin itself, followed by productivity losses from unemployment and disability, hepatitis C treatment, incarceration, and crime. An incarcerated heroin user cost society an estimated $74,400 per year, driven mainly by the cost of imprisonment and lost productivity.²⁴ In Taiwan, the economic burden was calculated at about $18,300 per person per year, roughly equal to the country’s average per-capita GDP, with the cost of the drugs themselves representing the majority of direct expenses.²⁵ Quality of life among heroin-dependent individuals was poorer than that of healthy controls across every measured domain. These costs apply to heroin use disorder broadly, not to smoking as a distinct route, but they provide context for why reducing initiation and supporting treatment matters at a population level.