Upon use, individuals feel the effects of heroin almost immediately. Users quickly experience an intense rush of euphoria, as well as relief from anxiety, stress, and pain.

Once heroin enters the bloodstream, it binds to and activates opioid receptors in the brain, releasing endorphins (“feel good” hormones) that trigger a sense of euphoria and block pain signals. After this initial surge of euphoria, users may experience a dream-like state. Breathing, heart rate, motor and cognitive functions, and reactions slow down, while the user becomes drowsy and lethargic. Dangerous levels of respiratory depression are possible, which can lead to coma, brain damage, or death.

When the pleasure and reward center of the brain is activated naturally, the body releases endorphins and dopamine in response to a pleasant experience. Heroin causes a much more intense physical and emotional response, strongly reinforcing the behavior.

Continued heroin use causes the body to adapt to the drug’s presence, creating an imbalance in the brain. This adaptation results in a demand for increasingly higher doses of heroin to achieve the desired effect. This is called tolerance, which is a sign of addiction. Once tolerance sets in, if an individual abruptly stops their drug use, they will likely experience withdrawal symptoms.

The National Institute on Drug Abuse (NIDA) website states heroin withdrawal symptoms may include restlessness, muscle and bone pain, insomnia, diarrhea, vomiting, cold flashes with goosebumps, and leg movements. While withdrawal symptoms typically last about a week, peaking 24–48 hours after the last dose of heroin, some individuals continue to experience symptoms for several months.

Regular, long-term use of heroin can cause devastating physical and psychological damage. Over time, the brain becomes unable to naturally produce the chemicals that regulate mood and pleasure, so the user can only feel good, or even “normal,” by using heroin.

Heroin use has the potential to damage numerous functions of the brain, many of them life-sustaining. Areas of damage may include the:

• Central nervous system (CNS), which is made up of the brain and spinal cord. The CNS controls awareness, sensations, movement, thought, speech, and memory.
• Brain stem, which controls sleep, breathing, swallowing, heart rate, blood pressure, and consciousness.
• Limbic system, which controls the reward and motivation center of the brain. This system regulates emotions, memories, and arousal.
• Cerebral cortex, which controls thinking, problem solving, decision making, and the ability to process information. This region also controls the senses.

Multiple research studies have found that regular heroin use causes the brain’s white matter to deteriorate, contributing to impaired decision making, judgment, ability to handle stress, and impulse control. This puts heroin users at an increased risk for severe depression, risky decision making, and suicide. This damage to the brain may be irreversible.

In addition to brain damage, continued heroin use may cause damage to the heart, liver, kidneys, reproductive system, and digestive system. Chronic insomnia may occur in all users, as well as sexual dysfunction in men. Users who inject heroin are at increased risk for skin or other bacterial and fungal infections, collapsed veins, skin abscesses, and diseases like HIV/AIDS, Hepatitis B, and Hepatitis C.

NIDA warns that regular heroin use often leads to heroin use disorder, which is defined as “a chronic relapsing disease that goes beyond physical dependence and is characterized by uncontrollable drug-seeking, no matter the consequences.” According to NIDA, at this point, drug-seeking becomes the user’s primary goal in life, and it is unlikely the user can quit without professional assistance.