What are Opioids?

Opioids have similar properties to the opium from which they are derived. One of the main functions of opioids is to produce sedation and pain relief and they have been used for pain relief over thousands of years. Opioids are essentially chemicals that bind to opioids receptors present in the brain and central nervous system and the gastrointestinal tract to stimulate their effects.

Opium plant (Papaver somniferum)

Opioids as pain relievers

One of the most common uses of opioids is pain relief. The pain relief produced leads to several features in the recipient:

  • The perception of pain is reduced making the person feel that pain is less intense
  • The reaction to pain is reduced
  • Pain tolerance is increased

Other effects and side effects of opioids

In addition to pain relief, there are several effects mediated by opioid receptors present in the central nervous system and the gastrointestinal tract. These include:

  • Sedation or drowsiness: This makes the driving and operation of heavy machinery dangerous for people on opioids.
  • Suppression of cough: Opioids suppress the cough reflex in the brain leading to suppression of a cough. Opioids such as codeine have therefore long been used as cough suppressant.
  • Respiratory depression: This describes suppression of the breathing mechanism in response to low blood oxygen. As blood oxygen falls and blood levels of carbon dioxide rise, there is an increase in drive for respiration. However, opioids suppress the respiratory centre and drive in the brain, potentially leading to hypoventilation.
  • Constipation: One of the main side effects of opioids is constipation due to the sluggish persitalsis in the digestive tract that they cause.
  • Dependence and likelihood of abuse: Use of opioids in the long term may cause dependence on the drugs leading to withdrawal syndrome when an individual suddenly stops taking them.


  1. https://www.painphysicianjournal.com/
  2. http://www.britishpainsociety.org/book_opioid_patient.pdf
  3. http://www.uic.edu/classes/pcol/pcol331/dentalpharmhandouts2006/lecture51.pdf
  4. http://www.knowledge.scot.nhs.uk/home.aspx

Further Reading

Last Updated: Jun 19, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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