- the deaths cannot be due to overdose,
- there has never been any evidence that they are due to overdose,
- there has long been a plethora of evidence demonstrating they are not due to overdose.
To understand why people have claimed that it is a misnomer to attribute these deaths to the traditional understanding of "overdose", we have to look at the factors that influence the development of drug tolerance and why the usual processes of tolerance failed. Tolerance is usually defined as the decreasing effects of a drug through repeated administrations, but even as far back as the 60's researchers were arguing that a complete explanation of tolerance requires an element of learning. This was argued on the basis that there were findings that could only be explained from a learning perspective; for example, the observation that the analgesic effect of morphine can persist in rats even after a number of drug-free months3.
Due to the way we normally conceive of 'tolerance' and our reliance on the purely physiological model, the idea that learning affects our biological tolerance to drugs can be quite a difficult concept to get our heads around. However, after looking at how classical conditioning can affect our response to the placebo effect (and the functioning of our immune system), we can look at how classical conditioning could play a role in drug tolerance. By looking at how classical conditioning was proposed to work by Pavlov, with a previously neutral stimulus (e.g. a bell) being paired with a unconditioned stimulus (e.g. food) and the neutral stimulus taking on the value of the unconditioned stimulus to produce the same effects (the sound of the bell becoming capable of making a dog salivate in the same way food does), we can begin to understand how classical conditioning could affect drug tolerance.