Pavlov's dogs made their name in psychology classrooms, but should probably be more famous for their physiology. A Pavlovian response is a physical, not psychological, reaction. And it's possible that that physical reaction is causing people to overdose on drugs in a very unexpected way.
When did Pavlov's dogs start salivating? When they heard a bell, you say? Au contraire. Pavlov's dogs started salivating when they saw lab coats. Workers at a lab that studied digestion noticed that the dogs used in the experiments were drooling for seemingly no reason at all.
It was only Ivan Pavlov, a scientist working at the lab, who made the connection between the lab coats and the drool. The dogs, Pavlov reasoned, knew that they were soon going to be fed whenever they saw a lab coat. What intrigued Pavlov was the fact that a physical response could be produced solely by way of a mental association. The dogs couldn't drool on command consciously, but they could be trained to do so just the same.
That's when Pavlov went to work with meat, dogs, and bells, and did the controlled experiment that earned him fame and fortune. He won a Nobel Prize in Medicine and Physiology for his research, but most of us hear about his famous experiment when we study psychology, not medicine. Once the Pavlovian response became a metaphor for an unthinking popular response to stimulus, it was divorced, in the public consciousness, from the physical reality. It shouldn't have been. The mind, when exposed to certain input, can prime the body into a specific state of physical readiness. This has physical, not just social or psychological, consequences.
There are a limited amount of places where one can do drugs. Of those places, drug users select a certain few places where they prefer to do drugs, and then do drugs most often at a select number of places that are convenient. Essentially, a regular drug user will often have a regular place to take their drugs. After they've done drugs regularly in the same place, the connection is made. A bathroom, a bedroom, a certain club, will always be associated with drug use. People trying to quit drugs often talk about how they have to avoid their old haunts, because they feel a rush of anticipation. That rush is not just mental.
Scientists learned that putting a dog in a certain injection booth every day and injecting it with adrenaline produced a dog with bradycardia - a dangerously slow heartbeat - when they put the dog in the same booth but only injected it with a placebo. The dog's body was compensating for the adrenaline it anticipated. It was trying to reduce the dangerous effects of the adrenaline by slowing down the dog's heartbeat.
A drug user's body does the same. Over time people build up a tolerance for the drug, not just because the body manages to deal with the drug when it's in their system, but because the body knows to prepare for the drug before it has been administered. When a person who has built up a tolerance for a drug in a certain place goes somewhere new, the body may not know what's coming to it, and that tolerance is greatly reduced.
In one experiment, scientists studied rats who had been given regular doses of heroin. Some of the rats were taken to a new area and given a larger dose of heroin. The others were injected with the larger dose, but kept in their regular environment. The mortality rate of the rats injected in a new environment was twice that of the rats injected in the familiar environment. No similar experiment of human drug users would be conscionable, but a survey of the survivors of heroin overdoses found that seven out of ten were in a new place when they overdosed.
Even the most basic functions our bodies perform are marvels of biochemistry. When the dogs salivated, they were releasing chemicals that would help them process their food. The biochemistry involving drugs is more complicated, and more vital, than digestion. When we're not careful, we can unwittingly train ourselves into Pavlovian responses that are dangerous to ignore.