How Do Opioids Affect The Brain

Orange County Detox
heroin effects on the brain

Opioid receptors:

Regardless if an opioid is a prescription painkiller like Oxycodone or an illicit opiate like Heroin, the effects typically depend upon how much you take, how long you’ve been taking it and how you administer it. If an opioid is injected, it will enter your bloodstream immediately, reach your brain rapidly, and respond more intensely. If an opioid is swallowed, it will take longer to enter your bloodstream, reach your brain more slowly, and respond with less intensity.


Actions of opioids

When heroin, fentanyl, or any other opioid enters the brain, they disperse and bump into tiny proteins atop neurons called receptors. Scientists discovered three receptor types that bind with opioids: mudelta, and kappa. Opioid friendly receptors are called opioid receptors and each type plays a different role. Opioids affect the brain because they bind to and activate μ-mu opioid receptors, which are the most prevalent opioid receptors in the human body and the receptors most responsible for opioid drug effects.

The following is a list of opioid drug effects.

  1. Analgesia – pain relief
  2. Euphoria – feeling of pleasure caused by increased dopamine
  3. Sedation – sedation generally precedes significant respiratory depression
  4. Respiratory depression – dual complimentary effects of mu and delta opioid receptors
  5. Cough suppression – antitussive
  6. Anti-diarrheal – causes constipation


If a person administers 30 mg of heroin there is a fairly high likelihood of an overdose, and if that same person were to administer just 3mg of Fentanyl the potential for overdose would be about equal. The reason being that Fentanyl, which is a man-made opioid, has high responsivity with mu-opioid receptors. The mu opioid receptor is considered the most important, since this type produces the majority of analgesic, antitussive and antidiarrheal effects.

Opioid Effects

The following three regions hold the majority of Central Nervous System (CNS) opioid receptors and therefore produce the majority of opioid effects overall.

  1. Limbic system: Opioids create the sensation of pleasure, relax muscles, and produce feelings of contentment.
  2. Brainstem: Opioids slow breathing, stop coughing, and reduce pain.
  3. Spinal cord: Opioids reduce pain.



Opioid Interneuron

What is an interneuron?

Neurons are nerve cells. Interneurons, as shown above, are nerve circuits i.e. two or more neurons working together to create a specific response. Interneurons are primarily found in the brain, brainstem and spinal cord and they carry the information that allows us to think, act, learn, and feel.

A good way to think of a neuron is to think of a tree, with roots, a trunk and branches. The roots, or dendrites, are the main apparatus for receiving information. This information passes through the base of the trunk, or cell body, which processes the information. The processed information is sent up the trunk, or axon, which disperses the new information through the branches, or axon terminals, which releases the new information as falling leaves, or neurotransmitters, out to other neurons and so on and so forth.



Opiates like morphine and synthetic analogs opioids like fentanyl, are used in the treatment of acute and chronic pain. Scientific studies show that morphine and other opioids act upon neuron circuits and opioidergic systems. Not only do opioids control pain, they also produce pleasure and modulate gastrointestinal, endocrine, autonomic and cognitive functions.


Repeated administration of opioids:

An opiate or synthetic analog opioid will attach to the same opioid receptors as endorphins, that is to say, opiates and opioids exert their drug effects by mimicking endorphins. Your body’s endorphins are your private stock of narcotics. Endorphins are released by the pituitary gland in response to stress or pain. However, opiates and synthetic opioids are much stronger than endorphins, and therefore produce much greater drug effects.

One of the side effects of repeated opioid use is suppression of endorphin production. Consequently you become depleted of endorphins. In time, you will not have an adequate supply of natural painkillers, if and when you need them.

Another common side effect of opiate use is the development of hyperalgesia, which is a greater sensitivity to pain. Things that normally never caused you pain, suddenly do cause you pain. This is the paradox of opiate drug use. At first everything is great, then suddenly, you’re miserable without them.


Adverse drug effects

The euphoric, analgesic, sedative and respiratory effects of opiates have been known since early history. However, unintended sedation and respiratory depression are two of the most serious problems when people use opioids, and this is what limits its safety and usefulness. There is another factor that’s often overlooked, that opioids kill people and not just by overdose. Some people fall down and hit their head while others crash their car. In fact, no other medication kills more people.


Opioid side effects

Opioids may cause side effects on the cardiovascular system, thermoregulation, hormone secretion and immune function. However, multiple factors, such as opiate type, dose, formulation, route of administration, duration of therapy, concomitant medications, and general health, can influence the occurrence of side effects. Major side-effects associated with opioid use include the following:


Short-term Side Effects

  1. Constipation – common side effect unaffected by tolerance
  2. Urine retention – common side effect unaffected by tolerance
  3. Pinpoint pupils – common side effect unaffected by tolerance
  4. Nausea – common side effect, that may require anti-nauseants
  5. Wheal, flare and itchiness reactions on skin
  6. Decreased secretion of norepinephrine
  7. Hypotension –  low blood pressure
  8. Tachycardia


Long-term Side Effects 

  1. Tolerance
  2. Dependence- susceptible to withdrawal
  3. Addiction- compulsive seeking and using
  4. Lower testosterone levels – side effect of suppressed hypothalamus
  5. Skipped menses
  6. Decreased conative ability
  7. Decreased cognitive ability
  8. Impaired short-term memory
  9. Delayed verbal memory
  10. Increased secretion of norepinephrine


Hazards of opioids

The most dangerous effect of opiate use is overdose. Opiate overdose fatality is defined as a fatality due to respiratory failure following opiate consumption. Overdose occurs when the brain centers that control respiration relax and forget to breath. This results in periodic gasping for air. Eventually the brain forgets to gasp, which results in respiratory failure and eventual death. Studies suggest that on average opioid overdose takes approximately 3 hours. On the other hand, opioid toxicity fatality can result in death in just a couple of minutes.


Signs of Opioid Overdose:

  1. Unresponsive
  2. Fixed pinpoint size pupils
  3. Respiratory depression
  4. Shallow Respiration
  5. Gasping for air
  6. Low Blood Pressure
  7. Slow heart rate
  8. Clammy and cold skin
  9. Bluish skin
  10. Bluish fingernails
  11. Seizures


Key Terms:

dopamine (DA): Dopamine is a neurotransmitter synthesized from tyrosine in various regions of the brain and is involved in many neurological pathways and processes. Dopamine is an inhibitory neurotransmitter, meaning that when it finds its way to its receptor sites, it blocks the tendency of that neuron to fire.  Dopamine is present in brain regions that regulate movement, emotion, motivation, and the feeling of pleasure. As it turns out, dopamine plays a fundamental role in almost all aspects of human behavior: from motor control to mood regulation, cognition, addiction, and reward. The general rule is, if it feels good, dopamine neurotransmitters are probably involved. Drugs like heroin, alcohol, cocaine and nicotine all increase the brain’s release of dopamine. Dopamine is responsible for the motivation required to seek pleasure while opioid systems are accountable for our experience of pleasure. Thus dopamine is needed for “wanting”, while opioids are necessary for “liking”.

locus ceruleus (LC): A region of the brain that receives and processes sensory signals from all areas of the body; involved in arousal and vigilance.

μ-mu opioid receptor: A receptor on the surface membrane of nerve cells that mediates opioid analgesia, tolerance, and addiction. Opioids affect your brain because they cross the blood brain barrier then bind to and activate μ-mu opioid receptors, the receptor most responsible for opioid affects.

norepinephrine (NE): A neurotransmitter produced in the brain and peripheral nervous system; involved in arousal and regulation of blood pressure, sleep, and mood; also called noradrenaline.

ventral tegmental area (VTA):  The ventral tegmental area, or VTA, is a group of neurons in the midbrain. The VTA is primarily characterized by its dopaminergic neurons, which is considered an integral part of the body’s reward system, which is involved in reinforcing behavior.