When a person believes they are receiving a helpful medicine that will cure their ills, the brain forms that expectation, and those thoughts induce a physiological response in the body that produces antibodies and other natural drugs that often work better than the real thing. A person who believes they are drinking alcohol (which is in reality only tonic water) will behave just as a drunk might. This belief can actually cause the brain to respond accordingly, bringing about very legitimate mental and motor impairments. Meanwhile, those who are given actual alcohol to drink but who believe it is tonic water will tend to behave more normally, and actually outperform their tonic-water drinking counterparts on impairment tests. (Lang et al., 1975) So belief can not only work just like a drug, it can actually counteract it.
Pregnant women who were complaining of nausea were told about this wonderful new anti-nausea drug that worked miracles. They were then given Ipecac syrup, something you probably know is a drug given to induce vomiting, used when a person has swallowed a poison. Despite this, their belief about what the drug would do caused their body to override the chemical agents of the drug itself, and most of these women felt significant nausea relief after taking it. (Wolf, 1950) In other studies, a person who is told they are receiving a shot that is going to make a painful procedure more painful will actually experience more pain than a control group who received no shots, even though the shot they received was a local pain killer that should have numbed their pain. As psychiatrist David Spiegel points out, “it all boils down to expectation. If you expect pain to diminish, the brain releases natural pain-killers. If you expect pain to get worse, the brain shuts off the processes that provide pain relief. Somehow, anticipation trips the same neural wires as actual treatment does.” (in Erdmann, 2008, p. 26)