The nocebo effect: patients suffered more when told the drug was stopped, even though it continued to flow.
Volunteers in an MRI scanner had heat enough heat applied to their leg so they rated the pain around 70 on a scale of 1 to 100. An intravenous line for administration of a potent opioid drug for pain relief was also introduced.
When patients received the drug without being told, the average initial pain rating of 66 went down to 55.
They were then told that the drug would start being administered, although no change was actually made and they continued receiving the opioid at the same dose. The average pain ratings dropped to 39.
Finally, the volunteers were led to believe the drug had been stopped and cautioned that there may be a possible increase in pain. Again, the drug was still being administered in the same way with no change. Their pain intensity increased to 64. That is, the pain was as great as in the absence of any pain relief at the beginning of the experiment.
MRI scans showed that the brain's pain networks responded and matched their reports of pain.