Conditioning and Drug Tolerance

One form of unconscious learning that appears to be due to classical conditioning is drug tolerance Drug-taking behavior (such as using a needle or even opening a bottle of beer) functions as a signal or CS that predicts the introduction of the drug into the body. Eventually the act of drug taking triggers an anticipatory response: the secretion of drug antagonists that help eliminate the drug from the body.

How does classical conditioning explain drug tolerance? What factors increase the risk of overdose from heroin, and how does this relate to the rat studies?

The ability of experienced drinkers to "hold their liquor" (consume a lot of alcohol without showing much effect) is a sign that the body is adapting to the drug. Classical conditioning has occurred. Alcohol-consumption now triggers a strong anti-drug action that reduces the effect of the drug. The same thing happens with cigarette smoking and coffee drinking. As a person becomes addicted, the drug has less and less effect.

Siegel and colleagues (1981) demonstrated that drug tolerance was due to classical conditioning. They gave rats morphine, a relative of heroin. Sometimes the rats received a signal followed by a period of no morphine. Therefore the signal indicated a drug-free period. Gradually the rats built up a tolerance to the morphine. Its pain-killing effects disappeared. But when morphine was given after the signal (typically a drug-free period) the rats had no tolerance for the morphine and the full pain-killing effects returned.

Intrigued by this finding, Siegel and co-workers (1982) gathered data on heroin overdose deaths in humans. They found that victims of heroin overdose were typically occasional or weekend users, not daily users. Often the fatal overdose occurred in unfamiliar environments. Drawing an analogy to their rat studies, the researchers proposed that addicts who took the drug in an unfamiliar setting, or took it after a period of time not using the drug were in special danger of overdosing. Their bodies failed to perform the usual anticipatory response of secreting opiate antagonists, so they had less tolerance.

What are possible reasons that Sid Vicious overdosed on heroin after being released from prison?

The punk rocker Sid Vicious, subject of the movie Sid and Nancy, died of a heroin overdose the day after being released from prison, pending trial for the murder of his girlfriend Nancy. He died upstairs in his mother's house. Probably there were two things that made his overdose more likely. He had been drug-free for several weeks while in prison, and his mother's house was not his usual drug-taking environment. Therefore a classically conditioned response did not take place. His body did not secrete opiate antagonists in the usual amount, and he did not tolerate his usual dosage of heroin.


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