Characteristics of placebo responses in medical treatment of premenstrual syndrome.

OBJECTIVE: This study characterizes the responses to placebo medication of patients with premenstrual syndrome (PMS) who were randomly assigned in controlled treatment trials. Possible predictors of placebo response were also examined.

METHOD: Subjects from two randomized controlled trials were pooled. The 101 subjects met defined criteria for severe PMS, remained eligible after 1 month of single-blind placebo lead-in treatment, and were randomly assigned to 3 months of double-blind placebo treatment. Improvement in the current study was defined as a decrease of at least 50% in premenstrual symptom score from the pretreatment baseline.

RESULTS: At endpoint, 20 (20%) of the placebo-treated subjects showed sustained improvement, 18 of these in at least 3 of the 4 months of placebo medication. Another 42% of subjects partially improved, and 39% were clearly unimproved throughout the study period.

CONCLUSIONS: Some patients with severe PMS experience significant and sustained improvement with placebo medication, but the majority report only partial or no improvement. Patients who sustain improvement for at least 2 consecutive months are likely to remain improved, indicating the importance of nondrug factors in clinical care.