Placebo and nocebo responses mystify, confound, and intrigue. They are social, cultural, and psychobiological events that have the ability to significantly impact the body.

The placebo effect is related to anticipatory anxiety and relief, whereas the nocebo effect is associated with a lack of reward/positive expectation and an increase in anticipatory fear.

Although the precise mechanism by which placebos work is unknown, it is believed to involve a complex neurobiological response involving everything from increased levels of feel-good neurotransmitters such as endorphins and dopamine to increased activity in specific brain regions associated with mood, emotional reactions, and self-awareness.

"Help, I've consumed all of my medicines." A 26-year-old man at the emergency room collapsed to the floor as his hands dropped an empty prescription bottle.

Mr. A, as he was referred to in his 2007 case study, regained consciousness but appeared pale-faced, sluggish, and lethargic. He told medics he ingested 29 capsules impulsively during a disagreement with his girlfriend—the pills were an experimental depression medication he was given in a research trial.

His blood pressure dropped extremely low, and his heart rate increased to a furious 110 beats per minute. He exhibited minimal improvement after four hours on an IV.

Then a physician in charge of the clinical experiment arrived. He stated that Mr. A was a member of the placebo group—patients who were randomly assigned to receive a drug that had no effect. Any symptoms he was experiencing were not due to the medications but to his imagination.

Mr. A "expressed shock and surprise, followed by nearly weeping relief." Within 15 minutes, his blood pressure returned to normal, as did his heart rate. He was back to normal.

Mr. A's hypotension appears to have been caused by the placebo overdose, according to the study. This phenomenon is often referred to as the nocebo effect.