Objective changes in intrauterine pressure during placebo treatment of dysmenorrhea

The paradoxical improvement of many subjective phenomena during placebo therapy is both well established and notorious for confounding many well designed studies. Consistently high placebo response rates of as much as 44% have been reported in subjective studies of dysmenorrhea. In an effort to evaluate the discordant role of objective uterine activity known to be associated with primary dysmenorrhea and the subjective sensation of discomfort, data from 18 patients undergoing meclofenamate therapy for primary dysmenorrhea were evaluated. In this study both the sum of pain intensity differences (SPID) and the total pain relief scores at each study time (TOTPAR) showed increases during both drug and placebo therapy with statistically significant differences favoring drug therapy. Ten percent of patients eventually reported 'complete relief' during placebo therapy. In contrast to this subjective placebo response, objective measures of intrauterine pressure showed consistent worsening in 13 out of 14 pressure parameters with 25% of patients experiencing a 2-fold or greater increase in the number of contractions while on placebo therapy. The ability to document unchanged or worsening objective parameters associated with the development of 'pain' in the face of reported subjective improvements may provide new insight into the mechanisms by which the 'placebo effect' occurs.