Heroin Side Effects

Heroin is an illegal opioid derived from morphine, a natural substance found in the seeds of the opium poppy plant. It’s one of the most addictive drugs in the world, and one of the most dangerous. People use heroin by injection, smoking, snorting, or rectal administration, with injection producing the fastest and most intense effects.

Knowing about what heroin use does to the brain and body in both the short and long term can help people recognize the signs of use and addiction in themselves or someone they care about.

How Does Heroin Work?

Heroin is a semi-synthetic opioid drug that acts as a depressant in the body. As a derivative of the natural opiate morphine, heroin is chemically similar to prescription opioids like codeine and oxycodone. As heroin enters the brain, it is converted to morphine and binds to the body’s opioid receptors, which are involved in the regulation of body movement, mood, hormones, and pain sensation.

Heroin is very fast-acting. The most common way people use heroin is by injection, followed by smoking, snorting, and plugging. Injecting heroin can cause euphoric effects within seconds.

What Are The Effects Of Heroin?

Heroin is a fast-acting drug that has a short half-life. This means it is rapidly absorbed and metabolized in the body, resulting in rapid but short-lived effects. When used, heroin can cause a range of short-term effects. Chronic heroin use may cause long-term effects on health, mood, and behavior.

Short Term Side Effects Of Heroin

Heroin is fast-acting, with effects that can be felt within seconds of injection and within minutes when smoked or snorted. The initial rush produces an intense wave of euphoria, warmth, and pain relief, followed by a prolonged state of sedation sometimes referred to as “going on the nod,” where a person drifts in and out of a semi-conscious state. Physical effects during this period include dry mouth, severely constricted pupils, flushed skin, heavy limbs, slowed heart rate and breathing, reduced blood pressure, nausea, and vomiting.

The short-lived nature of heroin’s effects, which typically wear off within a few hours, often drives users to take repeated doses in rapid succession, increasing the risk of overdose.

Learn more about the short-term effects of heroin

Long Term Effects Of Heroin

Chronic heroin use can have long-lasting effects on the brain and body, especially when the drug is used regularly and in high doses.

Over time, chronic use of heroin can lead to:

• increased tolerance
• physical dependence
• drug addiction
• abscesses (from injection)
• insomnia
• constipation
• changes in mood
• poor decision-making
• risk of infectious diseases (HIV/AIDS, hepatitis)
• heroin cravings

Developing a higher tolerance for heroin can require that you take higher doses over time to feel the desired effect. This can increase the risk of physical dependence and addiction.

Learn more about the long-term effects of heroin

Heroin Effects On The Body

Injecting, snorting, or smoking heroin can cause it to enter the brain within anywhere from a few seconds to minutes. This can cause rapid effects on the body.

Physical side effects of heroin can include:

• relaxation
• drowsiness
• dry mouth
• constricted (tiny) pupils
• nausea and vomiting
• flushed skin
• severe itching

The effects of heroin on the body can also include slower heart rate, reduced blood pressure, and slower breathing. People may drift in and out of a semi-conscious state, also referred to as going “on the nod”.

Learn more about the physical effects of heroin

Heroin Effects On The Brain

Heroin produces its effects as a result of how it interacts with the brain. Upon entering the brain, heroin is converted to morphine and binds to the body’s mu-opioid receptors.

Heroin can cause:

• feeling of pleasure
• warmth
• reduced pain
• decreased appetite
• changes in sleep

Although many people use heroin for its euphoric effects, heroin may also cause depression, anxiety, and worsened symptoms of mental illness.

Learn more about the effects of heroin on the brain

Heroin Dependence, Addiction, And Withdrawal

Heroin is one of the most physically and psychologically addictive substances known, and stopping without professional help is both difficult and dangerous.

Dependence

Physical dependence on heroin develops when the brain adapts to the drug’s presence and begins to rely on it to function normally. Once dependence develops, withdrawal symptoms can begin within 6 to 12 hours of the last dose, peaking around 36 to 72 hours and lasting anywhere from a week to several weeks depending on the severity and duration of use.

Common withdrawal symptoms include intense cravings, muscle and bone pain, nausea, vomiting, diarrhea, sweating, chills, insomnia, and severe anxiety, often described as one of the most physically uncomfortable experiences a person can go through.

Addiction

Heroin addiction goes beyond physical dependence. It’s a chronic condition that changes how the brain processes reward, motivation, and decision-making, making it difficult to stop even when someone wants to. Polydrug abuse, where heroin is combined with other substances like benzodiazepines, alcohol, or cocaine, complicates withdrawal and raises the risk of dangerous and unpredictable symptoms that require immediate medical attention.

Withdrawal

Attempting to detox from heroin cold turkey without medical supervision is strongly discouraged. Unsupported withdrawal dramatically increases the risk of relapse, and relapse after a period of abstinence is dangerous because tolerance drops quickly, meaning the same dose a person was previously taking can now cause a fatal overdose. Medically supervised detox programs use medications like methadone, buprenorphine, and clonidine to manage withdrawal symptoms safely, reduce cravings, and lay the groundwork for longer-term recovery.

What Factors Can Influence The Effects Of Heroin?

Heroin doesn’t affect everyone the same. Different types of heroin, such as black tar heroin and heroin mixed with other drugs can also cause variance in side effects.

Factors that can influence the effects of heroin include:

• type of heroin
• amount used
• frequency of use
• additives in heroin
• polysubstance use
• co-occurring physical and mental health conditions
• drug dependence

These and other factors can make the effects of heroin more potent and potentially increase the chance of overdose.

Heroin Overdose

Overdose is a severe side effect of substance use that can occur if someone has taken too much of one or more drugs at once. Overdose can have dangerous effects on breathing, heart function, and blood pressure.

Risk factors for overdose include:

• taking fentanyl-laced heroin
• taking other drugs with heroin (including alcohol)
• injecting heroin
• using heroin after detoxing

Heroin overdose can be deadly. Administering the drug naloxone (Narcan) can reverse a heroin overdose by blocking the effects of heroin in the brain.

Treatment For Heroin Addiction

People who use heroin may become addicted to the drug through chronic use. Once addicted, it can be physically and psychologically difficult to quit alone. Professional treatment for heroin addiction can help.

Common treatments for heroin addiction include:

• detox programs
• medications for opioid use disorder (e.g. methadone, buprenorphine, naltrexone)
• cognitive behavioral therapy (CBT)
• dialectical behavior therapy (DBT)
• group therapy
• individual therapy
• support groups such as Narcotics Anonymous (NA)

For more information about the effects of heroin and addiction treatment options, browse our directory or reach out to the Substance Abuse and Mental Health Services Administration (SAMHSA).