This is the 2007 version. Click here for the 2017 chapter 02 table of contents.


In 1976, the normally staid journal Science reported in a large headline that researchers were "High on Endogenous Opiates" (Marx, 1976). The pun was intentional because scientists were excited about their discovery of endogenous opiates, variously called enkephalins and endorphins. These are naturally occurring substances that resemble morphine and heroin. The word endogenous means naturally occurring within the body. Opiates are drugs in the same chemical family as opium (such as morphine and heroin).

What are "endogenous opiates" and what effect do they have?

Like other opiates, endorphins are painkillers. The body produces them in response to stressful events such as unavoidable electric shocks, sudden injury, or when pregnant women go into labor. Soldiers generate endorphins in their own bodies when they go into battle, which partly explains the ability of some to continue fighting despite injuries. In general,stress raises endorphin levels. For example, if researchers expose rats to inescapable footshock in an electrified metal cage, the rats' endorphin levels rise.

What type of stimulus produces endorphin release? What does not?

One might assume that endorphins are an automatic response to pain, but apparently this is not the case. Early endorphin researchers were surprised to find that a laboratory test that produces acute pain, dipping an arm into ice water, produced no change in endorphin levels (Grevert and Goldstein, 1978). Perhaps the laboratory situation separates stress from pain. It is painful but not stressful, because subjects realize it is an experiment and will soon be stopped. This meshes well with an insight discussed several times later in the book, namely, that psychological distress rather than physical pain causes "stress" as most people use the term. Stress requires negative emotions that are not necessarily present when dunking an arm in ice water for the sake of science.

How are endorphins misunderstood?

Endorphins have become widely known. Inevitably, they have acquired a popular image that does not correspond to reality. For example, one musician commented in an interview that he felt "a little burst of endorphins in my brain" when improvising with other musicians. No doubt he meant that he felt joy in creating music through improvisation. If he really experienced a burst of endorphins, he would feel numb, not excited. Endorphins are not pleasure chemicals; they are painkillers.

What is evidence that endorphins do not produce the jogger's high?

Another myth is that endorphins are responsible for the jogger's high reported by long-distance runners. The idea is plausible: long-distance running is a form of stress on the body that might conceivably produce endorphins. However, this is a case of physical stress not accompanied by negative emotions. Sure enough, research showed that jogging was not accompanied by bursts of endorphins. When joggers were given naloxone, a substance that blocks endorphins, they continued to experience a runner's high (Trotter, 1984).

How did research with naloxone demonstrate about placebo based pain relief?

The same sort of experiment shows that endorphins are produced by pain-killing placebo effects (pain relief due to belief in a medical treatment). Levine and colleagues gave naloxone, which prevents the effect of endorphins, to half the patients who received a sugar pill placebo at a dental appointment. When patients did not receive the naloxone, they experienced pain relief from the sugar pill. It was equivalent to a standard hospital dose of morphine, although it was entirely self-generated. When they received naloxone, this effect did not occur (Placebo's effect on pain may equal a dose of morphine, 1987).

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