"In clinical trials of drug treatments for women's sexual dysfunction, placebo responses have often been substantial," write Andrea Bradford, PhD, from Baylor College of Medicine in Houston, Texas, and Cindy M. Meston, PhD, from the University of Texas at Austin. "However, little is known about the clinical significance, specificity, predictors, and potential mechanisms of placebo response in sexual dysfunction."
The goal of the study was to evaluate the characteristics and predictors of sexual function outcomes in 50 women with FSAD who were randomly assigned to the placebo group of a 12-week, multisite, controlled pharmaceutical trial. Magnitude, domain specificity, and clinical significance of sexual function scores were evaluated at baseline and at 4, 8, and 12 weeks (after study completion).
Change with time in sexual function outcomes was assessed in relationship to several variables, including age and symptom-related distress at baseline, as well as changes in frequency of sexual behavior during the trial. The primary study endpoint was the total score on the Female Sexual Function Index.
"It's important to note that, even though these women received placebo, they all had an opportunity to talk to a health provider about their difficulties and were asked to closely monitor their sexual behavior and feelings over a 12-week period," Dr. Bradford said in a news release. "Just taking part in this study probably started some meaningful conversations."
Approximately one third of women receiving placebo had a clinically significant magnitude of change after study completion, with similar effect sizes across multiple aspects of sexual function. Although symptom improvement was strongly associated with the frequency of satisfying sexual encounters (SSEs) during treatment, there was significant variation between participants in the association between frequency of sexual encounters and outcome.
"Our study shows that even a limited intervention can have a positive effect in many women with sexual dysfunction," Dr. Bradford said. "This comes as no surprise to sex therapists, but it does suggest a need to investigate behavioral factors more closely in clinical trials."
Limitations of this study include observational design, precluding determination of causality; and the possibility that SSE frequency was just a proxy for another variable, such as changes in general relationship functioning. In addition, the retrospective analysis prevented direct manipulation of variables of interest, and it is not known whether trial participants who received no treatment would have reported the same effects as participants who received placebo.
"A substantial number of women experienced clinically significant improvement in sexual function during treatment with placebo," the study authors write. "Changes in sexual behavior during the trial, more so than participant age or symptom severity at baseline, appeared to be an important determinant of outcome. Contextual and procedural aspects of the clinical trial may have influenced outcomes in the absence of an active drug treatment."
Eli Lilly/ICOS shared the data set used in this study. This study was supported in part by the Houston VA HSR&D Center of Excellence. The views expressed in the journal article are those of the study authors and do not necessarily represent the views of the Department of Veterans Affairs. Drs. Bradford and Meston have disclosed no relevant financial relationships.
J Sex Med. Published online September 16, 2010.
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