Prior progestin studies treating hot flashes in women have been short duration and single dose. This study tests the progestin megestrol acetate (MA) at two doses versus placebo over 6 months.

Patients with T1-3, N0-1, M0 breast cancer were eligible after completion of surgery and chemotherapy and at least 4 months of tamoxifen (if prescribed). Women were required to have at least 10 hot flashes of any severity or at least five severe episodes per week. Patients were randomly assigned to placebo, MA 20 mg, or MA 40 mg for 3 months. Success at 3 months was defined as completion of treatment with a >or= 75% reduction in hot flashes from baseline. If success was achieved, drug treatment for another 3 months was given on the same blinded arm; if not, open-label MA 20 mg was added to blinded study drug and continued for 3 months. Other menopausal symptoms were also assessed.

Two hundred eighty eight eligible women were randomly assigned (286 eligible), of whom 85% were on tamoxifen, 40% had over 63 hot flashes/week, and 75% had vasomotor symptoms for >or= 6 months. Success at 3 months was 14% on placebo, 65% on 20 mg, and 48% on 40 mg (both MA doses superior to placebo; P < .0001). Most successes at 3 months were maintained at 6 months (77% on 20 mg and 81% on 40 mg).

MA significantly reduced vasomotor symptoms with durable benefit over 6 months. MA 20 mg/d is the preferred dose. There was no significant impact on other menopausal symptoms.