Opioid Receptors: How They Work

Last modified: September 23, 2013 01:03:25 PM

Opioid Receptors: How They Work

In the media, there is a lot of attention paid to prescription drugs like OxyContin and illegal substances like heroin, and the words opioids and opioid receptors get mentioned often.  However, in most cases these terms are not explained and the general public usually has no idea what opioids and opioid receptors are, and people usually don’t know why the opioids are so addictive.

First of all, opioids are semi-synthetic substances derived from the natural alkaloids found in the resin of the opium poppy.  An opiate, a term which is sometimes used as a synonym for opioid, is actually a subgroup within the opioid family.  Opioids are among the world’s oldest known drugs and their use predates the written word.

Opioid drugs, which include medications like Percocet, Vicodin and Oxycodone, alleviate pain all over the body by binding to the opioid receptors which are found in the spinal cord, the brain, and gastrointestinal tract.

What the opioid medications and illegal opioid drugs such as heroin do is interfere with the brain’s task of recognizing discomfort and pain once they get into the blood stream.  What makes these substances so highly addictive is their ability to stimulate the parts of the brain that deal with pleasurable and euphoric emotions; this is the “high” that some opioid users chase after.

There are four major types of opioid receptors; Nociception, delta, kappa, and mu.  All four can be found in the brain, but only mu receptors are found in the gastrointestinal tract and spinal cord as well as the brain.  Researchers believe that the mu receptor is the most important of the opioid receptors because it produces analgesia (pain suppression), reduced gastrointestinal function, respiratory depression, physical dependence and –most importantly for addicts – the feeling of euphoria.

When Opioids are used or abused for a long time, a tolerance for the drug gets developed, and the patient finds the need to ingest higher and higher doses to either achieve the characteristic “high” or pain-numbing effect.  This happens because of a process called endocytosis.  In endocytosis, the cell will internalize the opioid receptor, making far fewer opioid binding sites available on the surface of the cells to accept and receive the drugs.  With few receptors available, the dosage of opioid drugs will need to be ever increasing in order for the user to feel the same “high” or pain-relieving effects.

Withdrawal symptoms are intense and incredibly painful, causing intense suffering for the addict who is trying to kick the habit.  The pain is so terrible that many prefer to stay addicted to avoid the unpleasantness of withdrawal.  A person who is addicted and physically dependent on opioids should always seek professional medical help to deal with the withdrawal and resolve any underlying emotional or mental problems that can lead to a relapse in substance abuse behaviour.