Opioids are a powerful class of drugs used for the treatment of pain. Opioids also include illicit drugs that are not used to treat pain, such as heroin. In order to understand how opioids work, and what makes them so powerful, a little brain science is necessary.

Opioid and natural endorphin molecules compete to reach receptors on neurons.
Once they attach to the receptors, pain signals are blocked.

Endorphins

Endorphins were discovered in the 1970s when doctors were studying how opioids affect the brain. Endorphins are a type of neurotransmitter; a chemical that sends messages between neurons (nerve cells) in the brain. Neurotransmitters can either suppress or prompt a reaction, meaning they either tell the body to do something or stop it from doing something.

Endorphins, also called endogenous or “natural opioids,” are responsible for eliminating minor pain. For example, when a person hits his or her elbow on a door frame it may hurt briefly, but the brain immediately signals the release of endorphins to counteract the pain.

See When Are Opioids Appropriate?

Endorphins cannot counteract all pain. For example, pain from a broken bone or surgery typically require additional pain management.

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Opioid Medication: Explained

Opioids, such as morphine and oxycodone, are typically prescribed to people recovering from major surgery or to those who have been seriously injured. In these situations, endorphins are not strong enough to combat the pain.

When a person takes an opioid a series of events take place:

  1. Opioids—via pill, IV, injection, patch, or pain pump—enter the bloodstream.
  2. Once there, the opioid molecules bind to receptors, which are located on the end of nerves throughout the body, including the brain and spinal cord.
  3. The receptors are activated and either suppress or prompt a reaction. In this case, opioids will suppress pain signals from being transmitted.
    1. Receptors are also responsible for the other major effects of opioids, such as respiratory depression and constipation, which are also the result of receptor suppression.
  4. Opioids trigger the brain to release another neurotransmitter called dopamine.1 Dopamine is thought to be responsible for the euphoric feeling that people may associate with recreational opioid use.

See Types of Opioids

In the case of opioids, people may become physically dependent on a drug but that does not mean they are addicted. However, if a person is addicted to an opioid, he or she is likely physically dependent as well.

Dopamine is also responsible for encouraging the brain to repeat rewarding behavior,1 which is called reinforcement.

See Opioids’ Potential Risks and Side Effects

Dopamine and Opioids

There is a neurological process that occurs in the brain after taking an opioid that will occur in every person, regardless of outside variables, such as genetic, environmental, and social factors.

  • Taking opioids will result in an increase in dopamine production in a part of the brain called the limbic reward system.
  • The brain is wired so that it remembers rewarding experiences and makes them easier to repeat.
  • These mechanisms result in the formation of habits and reinforces the connection between taking an opioid and the pleasurable feeling associated with it.

The large amounts of dopamine produced by taking an opioid are strong enough that in some cases the brain is “taught” to seek out the drug even if it means making sacrifices in a person’s personal life, such as family and career.

Physical Dependence vs. Opioid Addiction

Physical dependence and opioid addiction are not the same. Addiction results in the unrestrained and compulsive use of a drug, while physical dependency does not.

Read more about The Difference Between Opioid Addiction and Physical Dependence

References:

  1. NIDA. Drugs, Brains, and Behavior: The Science of Addiction. National Institute on Drug Abuse website. https://www.drugabuse.gov/publications/drugs-brains-behavior-science-addiction. July 20, 2018. Accessed September 14, 2018.
Further Reading: Types of Opioids