Opiates are powerful
drugs derived from the poppy plant that have been used for centuries to
relieve pain. They include opium, heroin, morphine, and codeine. Even
centuries after their discovery, opiates are still the most effective pain
relievers available to physicians for treating pain.
Opiates elicit their powerful
effects by activating opiate receptors that are widely distributed
throughout the brain and body. Once an opiate reaches the brain, it quickly
activates the opiate receptors that are found in many brain regions and
produces an effect that correlates with the area of the brain involved.
Two important effects produced by
opiates, such as morphine, are pleasure (or reward) and pain relief. The
brain itself also produces substances known as endorphins that activate the
opiate receptors. Research indicates that endorphins are involved in many
things, including respiration, nausea, vomiting, pain modulation, and
Within the pleasure/reward system,
opiates activatete receptors in the VTA, nucleus accumbens, and cerebral
cortex. Research suggests that stimulation of opiate receptors by morphine
results in feelings of reward and activates the pleasure circuit by causing
greater amounts of dopamine to be released within the nucleus accumbens.
Opiates also act directly on the
respiratory center in the brainstem, where they cause a slowdown in
activity. This results in a decrease in breathing rate. When someone
overdoses on heroin, it is the action of heroin in the brainstem respiratory
centers that can cause the person to stop breathing and die.
The brain produces chemicals called
endorphins that have an important role in the relief or modulation of pain.
Sometimes, though, particularly when pain is severe, the brain does not
produce enough endorphins to provide pain relief. Opiates, such as morphine
are very powerful pain relieving medications. When used properly under the
care of a physician, opiates can relieve severe pain without causing
Feelings of pain are produced when
specialized nerves are activated by trauma to some part of the body, either
through injury or illness. These specialized nerves, which are located
throughout the body, carry the pain message to the spinal cord. After
reaching the spinal cord, the message is relayed to other neurons, some of
which carry it to the brain. Opiates help to relieve pain by acting in both
the spinal cord and brain.
At the level of the spinal cord,
opiates interfere with the transmission of the pain messages between neurons
and therefore prevent them from reaching the brain. This blockade of pain
messages protects a person from experiencing too much pain. This is known as
analgesia. Opiates also act in the brain to help relieve pain, but the way
in which they accomplish this is different than in the spinal cord. There
are several areas in the brain that are involved in interpreting pain
messages and in subjective responses to pain.
These brain regions are what allow
a person to know he or she is experiencing pain and that it is unpleasant.
Opiates also act in these brain regions, but they don't block the pain
messages themselves. Rather, they change the subjective experience of the
pain. This is why a person receiving morphine for pain maysay that they
still feel the pain but that it doesn't bother them anymore.
Although endorphins are not always
adequate to relieve pain, they are very important for survival. If an animal
or person is injured and needs to escape a harmful situation, it would be
difficult to do so while experiencing severe pain. However, endorphins that
are released immediately following an injury can provide enough pain relief
to allow escape from a harmful situation.
Later, when it is safe, the
endorphin levels decrease and intense pain may be felt. This also is
important for survival. If the endorphins continued to blunt the pain, it
would be easy to ignore an injury and then not seek medical care.