Environment Contributes To Drug Tolerance

For more than a decade, Texas A&M psychologist Antonio Cepeda-Benito has studied how learning facilitates the development of tolerance, and he says the environment in which a drug is consumed plays a large role in the drug's effects.

"If the same amount of a drug is administered in one context and later in another different and distinct context, then the effects of the drug are different," Cepeda-Benito says. "The drug has a much greater effect in a novel context rather than in a context that is associated with the administered drug."

Cepeda-Benito, who has studied morphine and nicotine's effects, terms this phenomenon "learned tolerance," and says gradual desensitization to a drug can be developed not only by repeated use of the drug, but also through a learning process that involves recognizing the environment.

In other words, a person consuming a drug in a setting where he or she usually consumes the drug or even expects to consume it will be less likely to feel the full effects of the drug, he says. However, if that same person takes the same amount of the drug in a setting where he or she doesn't normally take the drug, then the person is likely to feel a greater effect from the drug.

He says a familiar context can mean any familiar environment and/or actions, as well as timing. He also notes that the longer the interval between episodes, the greater the chance is of developing a learned tolerance.

Cepeda-Benito says this could possibly explain some drug overdoses in which the person didn't take a greater amount of the drug, but instead, took the drug in an unfamiliar setting, making the term "overdose" a misnomer.

"These are physiological changes mediated by psychological aspects," he says.

Much like a butcher working in a meat freezer who isn't affected by the cold while at work but can feel cold at home, Cepeda-Benito says, the body, over time, begins to prepare itself, through learning, for the environment it is used to consuming the drugs in, resulting in a lessening of the drug's effects.

"This is important because we know that tolerance is a symptom of drug dependence, and when you become tolerant to a drug, then you need to take more of the drug to get the effect you want," Cepeda-Benito says. "The more of the drug you take, the more physiologically dependent you become."