They say, attitude is everything in life. It appears that our attitudes also have a bearing on our reaction to pain medication.

When heat was applied to their feet, the group that expected no relief from pain, actually reported intense pain. The group that was briefed to expect pain relief from the drug, reported less pain, while the group that was told to expect moderate relief from pain, experienced relief in sink with their expectation.
This study clearly points out that pain management must address the psychology of patients as well and must encourage positive attitude in pain patients, in order to have better treatment outcomes. Further, information provided by doctors about a certain treatment has a very powerful effect on patient expectations, which directly influences treatment outcomes.
Source-Medindia