Heroin

Heroin (diacetylmorphine, also called diamorphine) is a highly addictive semi-synthetic opioid produced by chemically modifying morphine, a natural alkaloid extracted from the seed pod of the opium poppy. It first appeared commercially in 1898, marketed — wrongly — as a non-addictive substitute for morphine, and was later removed from legitimate medicine in the United States as its dependence liability became clear. On the illicit market it appears as a white or off-white powder, a brown powder, or a sticky dark substance known as black tar heroin, and its purity and contents are unpredictable from one batch to the next. The defining feature of today's illicit heroin supply is contamination: street "heroin" is frequently mixed with or replaced by illicitly manufactured fentanyl and, increasingly, the veterinary sedative xylazine, neither of which can be seen, smelled, or tasted. What is sold as heroin is therefore often far more potent and unpredictable than the buyer expects.

Heroin acts as a prodrug: after entering the body it rapidly crosses into the brain and is broken down into 6-monoacetylmorphine and morphine, which bind to and activate mu-opioid receptors. These receptors are part of the body's natural system for regulating pain, stress, and feelings of well-being. When opioids activate receptors in the brain's reward circuitry, they trigger a surge of dopamine that powerfully reinforces repeated use — a core driver of how opioid addiction takes hold. The same receptor activity that produces pain relief and euphoria also suppresses the brain stem, the region controlling automatic functions such as breathing and heart rate. This is why opioids slow and can ultimately stop respiration, and it is the mechanism behind fatal overdose. With repeated exposure the brain adapts, producing tolerance and physical dependence, so that the drug is increasingly needed simply to feel normal and stave off withdrawal.

Shortly after use, heroin typically produces an intense initial rush, often accompanied by warm flushing of the skin, a dry mouth, and a heavy feeling in the arms and legs. Nausea, vomiting, and severe itching are common. This is usually followed by a drowsy, clouded state lasting several hours, in which mental function is dulled, heart rate slows, and breathing becomes shallow and slowed — sometimes dangerously so. Severely depressed breathing can lead to loss of consciousness, coma, and permanent brain damage from lack of oxygen. With repeated use the body develops tolerance and dependence, and stopping abruptly brings on a withdrawal syndrome that, while rarely directly fatal on its own, is intensely difficult: restlessness, muscle and bone pain, insomnia, diarrhea, vomiting, cold flashes with goosebumps, and uncontrollable leg movements. Withdrawal can begin within hours of the last use, peak around one to two days later, and generally eases over about a week, though sleep problems and cravings can persist far longer.

The single greatest danger of illicit heroin is that its contents are unknowable. Across the United States, street opioids are frequently adulterated with or replaced by illicitly manufactured fentanyl, which is far more potent by weight and now drives the majority of opioid overdose deaths. The sedative xylazine ("tranq") is an increasingly common additive that does not respond to opioid-overdose reversal and can cause severe skin wounds. None of these can be detected by sight, smell, or taste, so the strength of any given batch is impossible to judge in advance. Overdose occurs when breathing slows or stops; warning signs include unresponsiveness, slow or absent breathing, gurgling or snoring sounds, and blue or grey lips or fingertips. Naloxone (Narcan) is an opioid-overdose reversal medication available over the counter in the U.S. since 2023; it can restore breathing within minutes, more than one dose may be needed when fentanyl is involved, and it is safe to give even if opioids turn out not to be the cause. Combining heroin with other depressants — alcohol, benzodiazepines such as Xanax or Valium, or other opioids — sharply raises the risk of fatal respiratory depression and is a frequent factor in deaths. Over the longer term, heroin carries a high risk of addiction, and injection adds risks of collapsed veins, serious heart and soft-tissue infections, and blood-borne viruses including HIV and hepatitis C from shared equipment. If you suspect an overdose, give naloxone if available and call 911 immediately. For poisoning guidance, call Poison Control at 1-800-222-1222; for substance-use support, the SAMHSA National Helpline is 1-800-662-4357.

rapid "rush" of euphoria, then twilight state of sleep/wakefulness; drowsiness, warm flushing, dry mouth, heavy extremities

tolerance, physical + psychological dependence, addiction

respiratory depression, constricted pupils, nausea; overdose → slow/shallow breathing, blue lips/nails, clammy skin, convulsions, coma, death (naloxone reverses)

none in US

synthesized + marketed by Bayer early 20th c. as a "less-addictive" morphine substitute + cough suppressant; later discontinued — [DEA-HEROIN/DEA Museum]