A pretty interesting article from Massey University a few years back attempts to understand how much of the placebo effect is related to the conditioning effect (when I take a drug, I am conditioned to believe I will feel better because of my surroundings, so I feel better) or the expectancy effect (when I take a drug, I expect that it will work, so I feel better).
A number of interesting conclusions come out of this, notably that our tolerance to drugs is associated to our surroundings (as an example, consider examples of "learned tolerance", whereby drugs like alcohol affect people differently depending on their surroundings, leading to overdoses for alcoholics who find themselves drinking in unfamiliar places).
But my favorite one concerns the fact that, like humans, rats exhibit the placebo effect. This can serve to root out the misconception that the placebo effect is some mystical, made-up response at a high intellectual level. Rather it is an innate physical mechanism which exists across the animal kingdom. This can help to explain its complete prevalence (and its relationship with confirmation bias) among those susceptible to believing pseudoscience, and the reason we have such a hard time getting rid of it.
Oceanographer, Mathemagician, and Interested Party