Effects of Heroin Addiction on the Nervous System

The effects of heroin addiction can be devasting. Dope, brown sugar, black tar—regardless of the term used, you probably have been told the recreational drug heroin is a dangerous, illegal substance. Do you know why? Heroin is an addictive drug that acts on the brain’s opioid receptors. Although it may decrease pain, it is not without consequence. Users are susceptible to reduced heart function, gastrointestinal distress, respiratory depression, overdose, and death. Continue reading to learn about the effects of heroin on the nervous system.

Effects of Heroin Addiction on the Nervous System

What is Heroin?

Heroin is a drug derived from morphine—a substance originating from the seed pod of opium poppy plants grown in Southeast and Southwest Asia, Mexico, and Colombia. It is classified as an opioid. Heroin comes in the form of brown powder, white powder, or sticky black tar. The color and consistency depend on what it is mixed with (i.e. sugars, powdered milk, quinine).

While heroin shares many similarities with the prescription opioids, oxycodone and hydrocodone, it is illegal and highly addictive because of its effects on the pleasure centers of the brain. The sense of euphoria it gives makes it a popular recreational drug that is less expensive alternative to abusing prescription opioids.

How is Heroin Used?

Heroine is most often injected directly into a vein to produce immediate effects. However, it can also be injected under the skin for the body to  gradually absorb. Snorting the heroin or inhaling it are other administration methods. All three ways are addictive and cause dangerous side effects.

Heroin Addiction, Tolerance, and Dependence

Over time, the effects of heroin are not as intense or pleasurable. The diminished or lack of response to a drug over time is tolerance. It is not equivalent to addiction, but tolerance to substance does create potential for addiction. Instead, tolerance is when the current drug dose is no longer sufficient to produce the desired response

Dependence is the body’s adaptation to a drug. A larger dose is required to produce an effect. When someone is dependent on a drug, discontinuing the substance will likely provoke withdrawal symptoms.

Tolerance and dependence turn into addiction when an uncontrollable urge to use the drug develops. It is the inability to stop using a drug, as it alters the brain’s pleasure center. Addiction is a brain disorder stemming from physiological changes.

How Heroin Acts On Opioid Receptors

Heroin belongs to a class of drugs (i.e. opioids) that are powerful pain relivers. Pain medications have their place in medicine. However, heroin is misused to get high rather than taken as pain control. Heroin, like all opioids, attach to opioid receptors on nerve cells in the body.

There are three types of opioid receptors: mu, delta, and kappa. Mu receptors facilitate pleasure and euphoria from opioids like heroin. Heroin also acts on other locations in the nervous system.

The Brain Stem

The brainstem is comprised of three structures—the midbrain, the pons, and the medulla oblongata. Together, these structures regulate bodily functions that occur automatically. Functions like breathing, heart rate, blood pressure, reflexes, digestion, and balance are possible because of this crucial part of the brain.

Heroin also acts on the brainstem because the brainstem is home to many opioid receptors. This is why heroin is known to cause respiratory depression and irregular breathing, amongst other side effects such as constipation, urinary retention, and it significantly impacts the cardiovascular system. Solely through its actions in the brain stem, heroin is related to the slowing of heart rate. According to the Archives of Internal Medicine, those who use heroin are more than twice as likely to have a heart attack because the sudden exposure to toxins blocks blood flow in the vessels.

Limbic System

The limbic system is responsible for emotions. It controls one’s ability to feel happiness. Upon exposure to heroin, the drug takes over the limbic system to trigger the release of dopamine—the “feel good” neurotransmitter. Heroin users continue taking the drug to recreate the sensation or “high.” The constant release of dopamine conditions the brain and body to engage in reinforcing behaviors.

Spinal Cord

Opioid receptors are located on the spinal cord. The spinal cord’s role is to deliver messages from the brain to other areas of the body. Pain signals are derived from the spinal cord. Heroin binds to these receptors and decreases feelings of pain. Even after serious injuries, heroin blocks pain messages.

Short Term Effects of Heroin: The Rush

When heroin is used, it is first converted to morphine by the body prior to binding to the opioid receptors. The immediate short term effects of heroin are referred to as “the rush.” The high or “the rush” is a sense of euphoria and pleasure as the heroin binds to the opioid receptors to trigger the release of dopamine. Following the high, the user goes in and out of consciousness described as nodding off. This is accompanied by flushing of the skin, severe itching, dry mouth, decreased mental ability, nausea, vomiting, and a heavy sensation in the limbs.

Long Term Effects of Heroin

Over time, heroin is associated with detrimental long term effects to the mind and body. Heroin interrupts the neurotransmitter and hormonal balance while altering the structure of the brain.

  • Insomnia
  • Constipation and abdominal pain
  • Sexual dysfunction
  • Irregular menstrual cycles for women
  • Infertility and miscarriage
  • Damaged nasal tissue (i.e. if sniffed or snorted)
  • Collapsed veins (i.e. if injected)
  • Abscesses and skin infections
  • HIV and hepatitis
  • Liver disease
  • Decreased white brain matter
  • Kidney disease
  • Lung disease and pneumonia
  • Heart disease
  • Infected heart valves
  • Arthritis

Many of the complications from long-term heroin use stem from drug paraphernalia. Sharing needles increases the risk of blood infections like HIV and hepatitis. Injections in general leave the body a host for infections. Infection travels through the bloodstream to infect the heart and lungs. The wounds at the injection sites are also likely to become infected. In severe cases, the infection progresses to the point where amputation is needed.

Milk powder, starch, sugar, and other additives in heroin clog the blood vessels in the heart, liver, lungs, brain, and kidneys, Muli-organ failure is a real possibility with long term heroin use.

Mood Changes With Heroin Use

Mood changes and disorders are secondary to heroin use. Sudden mood changes occur because heroin alters brain chemistry. Someone using heroin is prone to rapid mood swings, especially after the initial euphoria subsides. They tend to lash out in anger, are easily agitated, and irritable. The agitation increases if experiencing withdrawal symptoms.

Addiction heavily coincides with depression. Heroin addiction destroys relationships, physical health, work, school, and mental health. The majority of the time, differentiating whether underlying depression resulted in heroin addiction or if heroin addiction caused depression.

Additionally, those with underlying mental health disorders are more likely to use. Studies show that using heroin while having antisocial personality disorder leads to hallucinations and paranoia.

Effects of Heroin Addiction

Brain Damage From Heroin

Brain damage can occur from heroin use. Someone using heroin is prone to respiratory depression. Shallow, labored breathing interferes with oxygen levels. As the body is deprived of oxygen, the brain and other organs cannot function optimally. Studies show that the chronic use of heroin decreases the white matter in the brain. White matter allows the brain to receive signals from various nerve cells. Insufficient white matter is associated with cognitive impairment with deficits in inhibitory control, reward processing, memory, attention, and decision making—all skills necessary to overcome addiction. Over time, heroin causes extensive damage that mimics Alzheimer’s disease. The dementia and decline in cognitive function may or may not be reversable. Even with current studies, the reversibility remains unknown.  

Heroin Withdrawal

Those who are addicted or dependent on heroin experience painful symptoms when they stop taking the drug. Onset of symptoms typically occurs between 6 and 12 hours from the last dose. However, most have worst symptoms 1 to 3 days later. In severe cases, withdrawal lingers for several months. This is called post-acute withdrawal (PAWS) syndrome. The discomfort of withdrawal is why heroin is difficult to quit. Studies by the Intramural Research Program have established that conditioned cues such as environmental stimuli associated with withdrawal can trigger its symptoms. Having medical assistance during withdrawal is advised.  

The symptoms of withdrawal feel like the flu and include:  

  • Fever and Chills
  • Restlessness
  • Muscle pain and spasms
  • Bone pain
  • Difficulty sleeping
  • Diarrhea
  • Nausea and vomiting
  • Abdominal pain
  • Shaking
  • Mood changes (i.e. agitation, nervousness, depression)
  • Heroin cravings

Heroin Overdose

A heroin overdose is when its use precipitates a fatal or near fatal response. The amount of heroin to overdose is determined by individual tolerance. With its addictive nature, those who have been using long term develop a tolerance and require more of the drug to produce the desired effect. However, someone who has not taken heroin before or uses infrequently may only require a small dose of the drug to overdose.  

Heroin is illegally sold and some sources are more pure than others. Dealers often mix heroin with other substances as a selling tactic. Mixing heroin with substances such as powdered milk, sugar, laundry detergent, rat poison, talc, starch, and even crushed pain relievers makes it seem as if they are selling a larger amount of heroin than they really are. If the user is unaware of the ingredients, it is difficult to judge the strength. It is easy to overdose if their regular dose of heroin could be stronger if its more pure or mixed with other dangerous drugs.

Symptoms of a heroin overdose are:

  • Weak pulse
  • Low blood pressure
  • Pale skin
  • Shallow breathing and/or gasping for breath
  • Disorientation or altered mental state
  • Pinpoint pupils
  • Inability to stay awake
  • Discolored tongue
  • Constipation
  • Seizures
  • Coma

In the case of an overdose, the patient is given Naloxone. Naloxone reverses an overdose by binding to opioid receptors so that heroin cannot activate them.

Heroin (Opioid) Use Disorder

Opioid use disorder is described as addiction to drugs which produce analgesia or pain relief. The National Institute on Drug Abuse reports that nearly 626,000 people in the United States had an opioid use disorder in 2016.

The signs of heroin addiction begin with intense cravings and an uncontrollable urge to use the drug. This is followed by taking the drug in large amounts, unsuccessful attempts to stop drug use, and continuing to use despite physical and mental health problems. Heroin addiction interferes with relationships, work, and decision-making.

Who is at Risk?

Statistics prove that adults between the ages of 18 and 25 are more at risk in comparison to younger populations. The risk of opioid use disorder increases after high school. Susceptibility is greater for non-Hispanic makes than females. Coming from a lower-income household and using multiple drugs aside from heroin also increases risk.

Heroin Addiction Treatment

Heroin addiction is a serious condition. Those who are addicted should be monitored in a medical setting to assist with withdrawal symptoms. Overcoming heroin addiction requires a group effort with a team of medical professionals, mental health professionals, and social support.


The three types of medications are agonists, partial agonists, and antagonists.  Methadone is the most common medication. As a slow-acting opioid agonist, it prevents withdrawal symptoms when taken daily. The high it produces is not as intense as heroin.  

Buprenorphine is a partial opioid agonist which binds to opioid receptors, yet has a lesser response. It does not result in getting high. Naltrexone is an opioid antagonist that blocks the action on opioid receptors. Unlike methadone and buprenorphine, Naltrexone is not addictive.


In combination with medication, behavioral therapies benefit opioid use disorder. The primary form of behavioral therapy for heroin addiction is cognitive behavioral therapy. During cognitive behavioral therapy, a trained therapist works with the client to identify problematic behaviors and the false beliefs, maladaptive learning patterns, and cognitive distortions that drive them. The therapist then instills coping methods. Self-monitoring drug cravings is a focus in behavioral therapy.

Contingency Management

A popular intervention for heroin addiction is a behavioral therapy called contingency management. Contingency management is incentive based. The goal is to reinforce positive behavior such as drug abstinence with tangible rewards. An example of contingency management is voucher-based reinforcement. For every negative drug test, the patient receives a voucher with monetary value. The voucher can be exchanged for rewards like movie passes, food, and goods. As the number of negative drug tests increase, so does the value of the vouchers. However, a relapse decreases the value of the voucher. A similar program utilizing contingency management is prize incentives. Rather than vouchers, patients win cash prizes for every negative drug test. Studies confirm contingency management is successful in patients who are in therapy along with methadone treatment.


Li, W., Zhu, J., Li, Q., Ye, J., Chen, J., Liu, J., Li, Z., Li, Y., Yan, X., Wang, Y., & Wang, W. (2016). Brain white matter integrity in heroin addicts during methadone maintenance treatment is related to relapse propensity. Brain and behavior6(2), e00436. https://doi.org/10.1002/brb3.436

Sivanesan, E., Gitlin, M. C., & Candiotti, K. A. (2016). Opioid-induced Hallucinations: A Review of the Literature, Pathophysiology, Diagnosis, and Treatment. Anesthesia and analgesia123(4), 836–843. https://doi.org/10.1213/ANE.0000000000001417

Stephanie A. Carmack, Robin J. Keeley, Janaina C.M. Vendruscolo, Emily G. Lowery-Gionta, Hanbing Lu, George F. Koob, Elliot A. Stein, and Leandro F. Vendruscolo. Heroin addiction engages negative emotional learning brain circuits in rats.

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