Endorphin and enkephalin
Endorphin and enkephalin are the body's natural painkillers. When a person is injured, pain impulses travel up the spinal cord to the brain. The brain then releases endorphins and enkephalins. Enkephalins block pain signals in the spinal cord. Endorphins are thought to block pain principally at the brain stem. Both are morphine-like substances whose functions are similar to those of opium-based drugs.
Today, the word "endorphin" is used generically to describe both groups of painkillers. These naturally occurring opiates include enkephalins (methionine and leucine), endorphins (alpha, beta, gamma, and delta) and a growing number of synthetic (artificial) compounds.
Natural and Artificial Painkillers
In the mid-1960s scientists proposed theories that the opiate narcotics (opium, heroin, morphine) mimic the actions of naturally occurring chemicals within the brain. They believed that these narcotics act as painkillers by manipulating the brain's receivers for those naturally occurring substances.
In the late 1970s researchers learned that there are specific areas in the brain that control pain. It is those areas that opiates attach themselves to in order to perform their functions. It was only then that researchers were able to identify the two naturally occurring pain killers, endorphins and enkephalins. This offered opportunities for developing drugs similar in structure to the natural pain-killing substances.