Remember the nocebo effect? It's the flip side of placebos. Placebos can make people feel better or even relieve pain (to a certain extent). Nocebo happens when a placebo causes negative side-effects—nausea, racing heart, dizziness, etc. And here's one more weird thing to add to this veritable bonfire of weirdness: When we tell people about the possible negative side-effects of a real drug, that might make them more likely to experience those side-effects.
In one study, 50 patients with chronic back pain were randomly divided into two groups before a leg flexion test. One group was informed that the test could lead to a slight increase in pain, while the other group was instructed that the test would have no effect. Guess which group reported more pain and was able to perform significantly fewer leg flexions?
Another example from the report: Patients undergoing chemotherapy for cancer treatment who expect these drugs to trigger intense nausea and vomiting suffer far more after receiving the drugs than patients who don’t.
And, like placebos and classic nocebos, this isn't just "all in their head"—at least, not in the sense that they're making it up or deluding themselves. There are measurable physical effects to this stuff.
As science writer Steve Silberman says in the article I've quoted from above, what we're learning here is that the feedback we get from other people ("That might make you feel yucky" or "You look tired today") has a physical effect on us. It's a little insane. It's also worth thinking about when we talk about medical ethics. Full disclosure of what treatments you're getting and what the risks and benefits are is generally regarded as the ethically right way to practice medicine. And that's probably correct. But how do you balance that with what we know about placebo/nocebo? What happens when transparency keeps you from using a harmless placebo as a treatment? What happens when transparency makes you more likely to experience negative health outcomes? It's a strange, strange world and it's not always easy to make the right ethical choices.