This study is designed to evaluate the within-woman effect of oral micronized progesterone (Progesterone 300 mg at bedtime) on semi-quantitative menstrual flow measured by the DivaCup® (menstrual cup with volume indicators at 7.5, 15 and 30 ml) or by counting the number of soaked normal-sized sanitary products such as normal-sized tampons or pads as well as length of flow and frequency and severity of menstrual cramps (on a 0-4 scale) in women with hot flushes and night sweats who are qualified to enroll in the primary perimenopausal hot flush trial stratified by whether they are in Early or Late Perimenopause.

The study will be a double-masked, placebo-controlled 28-day (4 week) baseline, 84-day (12 week) experimental trial, with a maximum number of 125 potential enrollees, with stratified random therapy assignment by Early or Late Perimenopause. Participants who meet the inclusion criteria for the original Progesterone for Perimenopausal Vasomotor Symptoms Study will be invited to join this additional sub-study. As part of the primary trial they will be randomly assigned into either the Progesterone or placebo group on a 1:1 basis. Primary and secondary data will be collected continuously throughout the study by completion of the Daily Perimenopause Diary-flow starting at baseline and continuously throughout the study.

Inclusion Criteria:

• >35 to <58 years of age
• Willingness to participate in this sub-study
• Perimenopausal status either based on irregularity of menstrual periods, or by onset of hot flushes/night sweats in women with regular periods
• Ability and willingness to complete the -flow recording instrument
• Ability to understand, speak, read and write English.

Exclusion Criteria:

• Less than 35 or greater than 58 years of age
• More than 1-yr without menstrual flow at study enrollment, including those with a hysterectomy ± ovariectomy
• Peanut allergy (because peanut oil is used in the progesterone formulation)
• Current or recent (within 6-mo of study enrollment) use of hormonal therapies (estrogen, progesterone, progestin-releasing intrauterine device (IUD), hormonal contraceptives, hormonal fertility treatments), or plans to initiate use during the study period
• Planned pregnancy or fertility treatment during the study period
• Inability to understand, speak, read and write English