Heroin is a highly addictive opioid made from morphine, which comes from the seed pods of opium poppy plants. In the short term, it slows the brain and body: breathing and heart rate drop, thinking becomes clouded, and a person becomes drowsy for hours. With repeated use, heroin changes the brain’s structure, builds tolerance and physical dependence, and can damage the liver, kidneys, lungs, and veins. The most serious risk is overdose, when breathing slows or stops.
Knowing what heroin does to you helps a family see which effects ease after heroin stops and which do not. If someone you love is using, heroin addiction treatment can address both the drug and the damage.
How Heroin Enters the Brain
Once heroin enters the brain, it is converted back into morphine, which binds rapidly to opioid receptors, according to the National Institute on Drug Abuse (NIDA) [1]. Those receptors sit in areas that control pain, reward, and mood, and in the brain stem, which runs automatic functions such as breathing and heart rate.
That explains why heroin affects so many systems at once: the same action behind the high also slows breathing. How quickly those effects start and fade is covered in our chapter on how long does a heroin high last.
Short Term Effects of Heroin
The first effects of heroin are physical. NIDA lists warm flushing of the skin, dry mouth, and a heavy feeling in the arms and legs, often followed by nausea, vomiting, and severe itching. Other effects follow for several hours:
- Drowsiness and nodding off
- Clouded thinking and slow reactions
- Slowed heart rate
- Slowed breathing, which can become life-threatening
- Small, pinpoint pupils
These short-term effects can look like tiredness or illness to someone who does not know what to watch for. Heroin clears the body quickly, but its breakdown products can be detected for days, as our chapter on how long does heroin stay in your system explains.
Long Term Effects of Heroin on the Brain
Repeated heroin use changes the physical structure of the brain. NIDA reports that long-term use causes deterioration of the brain’s white matter, which may affect decision-making, the ability to regulate behavior, and responses to stress [2]. These changes help explain why stopping is so hard, even when a person wants to.
Tolerance and Physical Dependence
With continued use, the brain adapts. Tolerance means a person needs higher doses to get the same effect, and physical dependence means the body now relies on the drug. When heroin use stops, withdrawal symptoms such as restlessness, muscle and bone pain, vomiting, and insomnia set in. CAMH notes that addiction can develop within two to three weeks of regular use [3]. Families tend to notice this cycle of use and sickness first, often before they know what is causing it.
Heroin Use Disorder
The Centers for Disease Control and Prevention describes opioid use disorder as a chronic brain disorder, a pattern of opioid use that causes significant impairment or distress [4]. Heroin use disorder is the form of that condition tied to heroin. It is a medical condition rather than a failure of willpower, and like other chronic conditions, it responds to consistent treatment. Mental health conditions such as depression and anxiety often occur alongside it and need care at the same time. Treatment usually begins with getting through withdrawal safely, and our heroin withdrawal timeline shows what that looks like.
What Heroin Does to the Body Over Time
Heroin affects many organ systems with long-term use. MedlinePlus lists liver, kidney, and lung disease among the risks, along with collapsed veins and abscesses [5]. CAMH adds constipation, loss of sex drive, and missed or irregular periods.
Street heroin is rarely pure. The Drug Enforcement Administration notes that it can be cut with sugar, starch, powdered milk, or other drugs, and NIDA warns that additives which do not dissolve can clog blood vessels leading to the lungs, liver, kidneys, or brain. Families sometimes find the drug before they see these effects, and our chapter on what heroin looks like in powder and tar form can help identify it.
Injecting drugs carries its own risks. The CDC warns that people who inject drugs face serious, long-term viral infections such as HIV, hepatitis B, and hepatitis C, along with bacterial infections of the skin, bloodstream, and heart. Shared needles and other equipment spread these infections, and some cause lasting liver or heart damage even after heroin use ends.
Heroin Overdose and Opioid Overdose Risk
An overdose happens when heroin slows breathing so much that the brain does not get enough oxygen. MedlinePlus explains that this lack of oxygen can lead to coma or permanent brain damage. The CDC reports that most heroin now available in the United States is combined with illegally made fentanyl, and that nearly 92 percent of opioid overdose deaths in 2023 involved synthetic opioids, mainly fentanyl. Mixing heroin with alcohol or other sedating drugs raises the risk further.
Naloxone comes in two forms, a nasal spray and an injectable, and anyone can use it without medical training. The CDC says it can restore normal breathing within 2 to 3 minutes, and MedlinePlus notes that more than one dose may be needed. People who use heroin, and the families around them, can buy naloxone at a pharmacy and carry naloxone at all times. Our guide on how to administer Narcan walks through each step.
Which Effects Reverse When Heroin Stops
Many effects ease with time. Withdrawal symptoms usually peak within the first two days and fade over about a week. CAMH notes that brain changes from long-term use can take months or years to return to normal, and some people have ongoing sleep, mood, or concentration problems during that time. Long-term recovery gives the brain that time to heal.
Other damage may not fully reverse. Chronic infections, organ disease, and brain injury from an overdose can be permanent, which is why early treatment matters. Spotting the physical and behavioral signs of heroin use sooner shortens the time the body is exposed to that harm.
Risk Factors That Raise the Danger
Some situations make heroin use more dangerous. CAMH and other public health sources describe risk factors that include using heroin alone, combining it with alcohol or other drugs, using after a period of not using, when tolerance has dropped, and not knowing whether fentanyl is present. Each one raises the chance of a fatal overdose, and drug overdose deaths often involve more than one substance.
Frequently Asked Questions About Heroin’s Effects
Does Heroin Damage the Brain Permanently?
Long-term heroin use has been associated with changes in brain white matter that may affect decision-making, behavioral regulation, and responses to stress [2]. CAMH notes that brain functioning may take months or years to return toward normal after long-term heroin use stops [3], but recovery varies and the long-term significance of these changes is not fully understood. Brain injury caused by severe oxygen deprivation during an overdose can be permanent [5].
How Quickly Does Heroin Tolerance Develop?
Tolerance can build quickly with regular use, so a person needs more heroin to feel the same effect. Addiction can develop within two to three weeks of regular use. Tolerance drops after a break, which is why returning to a previous amount after time away carries a high risk of overdose.
Can the Body Heal After Heroin Use?
Many effects improve once heroin use stops. Physical symptoms of withdrawal fade within about a week, and brain function can improve over months of recovery. Some damage, such as chronic hepatitis C, organ disease, or brain injury from an overdose, needs ongoing medical care and may not fully reverse. Treatment helps protect what can heal.
Getting Help for Heroin Addiction
If you have noticed a sour or vinegar-like odor along with these changes, our chapter on what heroin smells like explains where it comes from.
What heroin does to the body is serious, but much of it can improve with care. MedlinePlus notes that treatment for heroin use disorder combines medicines with behavioral treatments, and a treatment plan often starts with medically supervised detox to treat withdrawal symptoms safely. The Substance Abuse and Mental Health Services Administration runs a free, confidential National Helpline at 1-800-662-4357, and anyone in crisis can call or text 988. When you are ready to talk about next steps, the admissions team at Bright Paths Recovery can walk you through addiction treatment options, including heroin treatment and medically supervised detox in Los Angeles.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. If someone is not breathing or cannot be woken, call 911 immediately.
Sources
- National Institute on Drug Abuse. What are the immediate (short-term) effects of heroin use? https://nida.nih.gov/publications/research-reports/heroin/what-are-immediate-short-term-effects-heroin-use
- National Institute on Drug Abuse. What are the long-term effects of heroin use? https://nida.nih.gov/publications/research-reports/heroin/what-are-long-term-effects-heroin-use
- Center for Addiction and Mental Health. Heroin. https://www.camh.ca/en/health-info/mental-illness-and-addiction-index/heroin
- Centers for Disease Control and Prevention. Heroin. https://www.cdc.gov/overdose-prevention/about/heroin.html
- MedlinePlus. Heroin. National Library of Medicine. https://medlineplus.gov/heroin.html
