Heroin is one of the most harmful substances a person can put in their body. It damages nearly every organ system, rewires the brain’s reward circuitry, and carries a high risk of fatal overdose with every use. In 2024 alone, heroin was involved in 2,743 overdose deaths in the United States, and that number underrepresents the full toll because it doesn’t capture deaths from infections, organ failure, or other complications that build over time.
What Heroin Does to Your Brain
Heroin is converted into active compounds that flood the brain’s opioid receptors, triggering a massive surge of dopamine in the striatum, the brain’s reward center. That dopamine rush is what produces the intense euphoria users describe. But the brain adapts quickly. Within days to weeks of repeated use, the receptors become less sensitive, meaning you need more of the drug to feel the same effect. This is tolerance, and it’s the first step toward dependence.
Once dependence sets in, the brain’s natural ability to produce feelings of pleasure and well-being is suppressed. Without the drug, everyday experiences feel flat or painful. This isn’t a matter of willpower. The brain’s chemistry has physically shifted, and restoring normal function takes months to years, even with treatment.
The Immediate Dangers of Each Use
The most acute risk of heroin is respiratory depression. Heroin suppresses the brainstem’s drive to breathe. At high enough doses, breathing slows to the point of stopping entirely. This is how most heroin overdose deaths happen, and it can occur within minutes of use.
What makes this especially dangerous today is the contamination of the heroin supply. Nationally, roughly half of all heroin samples now contain fentanyl, a synthetic opioid that is many times more potent. A person using what they believe is their usual dose may unknowingly take a lethal amount. Fentanyl contamination has been rising steadily across every category of street drugs, but heroin has the highest co-occurrence rate of any substance tested.
Beyond overdose, heroin slows heart rate, lowers blood pressure, and suppresses the gag reflex. Losing consciousness and choking on vomit is a common cause of death that doesn’t always show up in overdose statistics.
Long-Term Damage to Organs
Chronic heroin use causes widespread, cumulative harm. The lungs are particularly vulnerable. Heroin’s suppression of breathing creates conditions for pneumonia and tuberculosis, and the general decline in health that accompanies addiction makes it harder to fight off these infections.
Many of the additives in street heroin, things like talc, starch, or other fillers, don’t dissolve in blood. When injected, these particles travel through the bloodstream and lodge in the tiny vessels of the lungs, liver, kidneys, and brain. Over time, they block blood flow and kill small patches of tissue in those organs. This damage is irreversible.
People who inject heroin also face scarred and collapsed veins, abscesses, and bacterial infections that can spread to the heart valves. Infected heart valves, a condition called endocarditis, can require open-heart surgery and is frequently fatal if untreated.
Infectious Disease Risk
Sharing needles or injection equipment is one of the most efficient ways to transmit bloodborne infections. Hepatitis C is the biggest concern: each person who injects drugs and carries hepatitis C is estimated to infect 20 other people. In 2014, the majority of new hepatitis C infections in the U.S. occurred among people who inject drugs. Hepatitis B rates in this population were as high as 25%, despite the availability of an effective vaccine.
HIV transmission through shared needles remains a serious risk as well. Even people who don’t share needles face elevated infection risk because heroin use often leads to situations, including transactional sex, where other forms of transmission become more likely.
Withdrawal and Physical Dependence
Heroin withdrawal begins 8 to 24 hours after the last dose and typically lasts 4 to 10 days. Symptoms include severe muscle cramps, nausea and vomiting, diarrhea, hot and cold flushes, heavy sweating, insomnia, and intense anxiety. The eyes and nose run constantly. While heroin withdrawal is rarely fatal on its own in otherwise healthy adults, it is profoundly uncomfortable, and the fear of withdrawal is one of the strongest drivers of continued use.
The physical symptoms peak around days two and three, then gradually ease. But the psychological pull, cravings, depression, difficulty feeling pleasure, persists for weeks or months. This is why relapse rates are so high without ongoing support.
Effects During Pregnancy
Heroin use during pregnancy poses serious risks to both mother and baby. Babies exposed to heroin in the womb are more likely to be born premature, have restricted growth, and have low birth weight. After birth, these infants can develop neonatal abstinence syndrome, essentially going through drug withdrawal. Symptoms appear within 24 to 48 hours of delivery and include high-pitched crying, tremors, rapid breathing, poor feeding, vomiting, and diarrhea. Heroin withdrawal in newborns is particularly notable for severe gastrointestinal symptoms that can lead to dangerous dehydration.
The long-term outlook for affected infants includes increased risk of neurodevelopmental delays, behavioral challenges, and premature death. These consequences extend well beyond the newborn period.
Treatment Options That Work
Heroin use disorder is a treatable medical condition. Two medications, methadone and buprenorphine, are equally effective at reducing heroin use and helping people stay in treatment. Methadone may offer a slight edge in treatment retention for some people. A third option, naltrexone, can be as effective as buprenorphine at preventing relapse when taken consistently over a long period.
These medications work by either partially activating the same brain receptors heroin targets (reducing cravings without producing a high) or by blocking those receptors entirely so heroin has no effect. For people leaving jail or prison, starting medication-assisted treatment before release significantly improves the odds of staying in treatment afterward. Recovery is a long process, often measured in years rather than months, but sustained treatment dramatically improves survival and quality of life.