Natural Opiates

Definition of this class

Scientists classify substances according to chemical structure, action or source. Natural opiates are narcotic pain relievers extracted from plant material that act by binding to special opioid receptors in the human body. Natural opiates cause analgesia, sedation, euphoria and other side effects. Other opioids mimic this action and cause similar results.

Difference between an opiate and an opioid

An opioid is anything that binds to opioid receptors. An opiate is a relatively natural product that acts as an opioid. All opiates are opioids, but not all opioids are opiates.

The opium in the poppy plant Papaver somniferum contains several alkaloids, including morphine, codeine and thebaine. Morphine and codeine bind to these opioid receptors to relieve pain and cause euphoria. Scientists isolate and purify these alkaloids into esters to produce stronger opiates. Pharmacologists further modify the chemical structure of these alkaloids to create semi-synthetic opiates such as hydrocodone and oxycodone.

Opium, its alkaloids and esters, and semi-synthetic opioids are all opiates because they are all derived from the poppy plant. All opiates have a common source, similar chemical structure and bind to opioid receptors.

Scientists create synthetic opioids in the laboratory, using compounds unrelated to the poppy plant and its alkaloids. These synthetic opioids act similar to opiates but they are chemically unrelated so they are not true opiates.

Drugs in this class

Examples of natural opiates include

  • Morphine
  • Codeine
  • Thebaine

History of natural opiates

The use of natural opiates to relieve pain predates history. People learned how to extract powerful analgesics from the poppy plant, otherwise known as Papaver somniferum.

Natural opiates relieve pain but produce side effects that can be serious or life threatening in some cases. Problems associated with natural opiates include constipation, sedation, respiratory depression and the potential for abuse. Opium addiction was an epidemic in China and elsewhere for about two centuries, resulting in two wars with the British Empire and putting China's financial stability in peril.

Early pharmacologists looked for ways to alter opium so that it provided pain relief without side effects, especially addiction. Scientists isolated morphine in 1804 and realized it reduced withdrawal symptoms in opioid-dependent people. Drug manufacturers offered morphine as a remedy for opium addiction. Since morphine causes a more potent sense of euphoria, opium addicts gladly engaged in treatment.

Pharmacologists continued to modify the molecular structures of morphine, codeine and thebaine to create new opioids but scientists did not really understand how opioids relieve pain.

A big breakthrough in understanding how opiates work came in 1973, when a graduate student administered radioactive morphine and studied its route. Scientists discovered that opiates bind to specific receptors in the brain and in other various places throughout the body. Much of the research since this discovery has focused on identifying and characterizing these receptors, and understanding how they interact with opioids. More recently, scientists are learning how to clone these receptors.

Opioid receptors

Scientists have discovered as many as 17 opioid receptors in the human body but there are three main opioid receptors: mu, kappa and delta. The body's response to a particular opioid depends onto which type of receptor the drug binds. Morphine most notably attaches to the mu receptor, as does codeine.

There are four major types of opiate receptors, with the first three being most important when discussing natural opiates: mu, delta, kappa and nociceptin receptors. Researchers named these receptors using the first letter of the first opiate found to attach to it. For example, the mu receptor was so-named after researchers discovered morphine attached to it.

These receptors influence the opening of ion channels, which sometimes reduces the excitability of the neurons in your nervous system. Scientists believe this reduced excitability causes the euphoric feeling associated with opiates. The mu and delta receptors seem to mediate this effect.

General information about some opioids in this class

The resin, or latex sap, of the opium poppy contains alkaloids. Some of these alkaloids, specifically morphine and codeine, relieve pain. Pharmacologists call these substances "natural opiates." Morphine is the most abundant of opium's 24 alkaloids, not all of which relieve pain or cause euphoria.

Morphine was the first alkaloid to be isolated from opium. Morphine is the gold standard that doctors use to compare pain relievers. For example, a doctor might say that hydromorphone is 7 to 10 times stronger than morphine.

Morphine works by binding to the mu receptor. In fact, the mu receptor was named after the first letter of morphine; mu is the Greek letter "m."

Morphine has a sturdy molecular structure that allows scientists to modify it without losing any of its analgesic properties. As a result, pharmacologists have created numerous semi-synthetic opioids by manipulating the morphine molecule.

German scientist Friedrich Sertürner first isolated morphine from opium in 1804. He named morphine after the Greek god of dreams, Morpheus. Merck, a small chemist's shop at the time, introduced morphine in 1827. The invention of the hypodermic needle in 1857 popularized the use of morphine.

The hypodermic needle and morphine were instrumental in the American Civil War. Physicians were able to administer precise doses of morphine to soldiers who were unable to swallow a pill. While morphine and the hypodermic needle reduced the suffering of countless troops, thousands of soldiers became addicted, a condition known as "Soldier's disease."

Codeine is the second most predominate alkaloid in opium. French chemist Pierre Robiquet isolated codeine from opium in 1832. Codeine is the most widely used opiate in the world. Codeine works by binding to the mu receptor.

Another important alkaloid is thebaine, which pharmacologists use to create synthetic and semi-synthetic opioid drugs that relieve pain in a way similar to natural opiates.

Other plants contain natural opiates. The Salvia divinorum plant and leaves from Mitragyna speciosa, commonly known as kratom, contain this analgesic. Poppies are, however, have always been the plant of choice when it comes to relieving pain.

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