The purpose of this study is first, to compare the efficacy of calcium carbonate to fluoxetine in the treatment of moderate to severe PMS. Second, to compare each active agent to a placebo control. Third, to evaluate the efficacy of each treatment for specific symptom clusters (i.e. affective and somatic). Fourth, to determine whether the addition of calcium to on going fluoxetine treatment leads to additional therapeutic benefit.

This is a two-center, double blind, randomized, placebo controlled, parallel study that will randomize 120 women into treatment. Participants will be screened at various collaborating ob-gyn centers for possible PMS symptoms, and direct referrals from the community will also be accepted. Our site's targetted enrollment is 60 subjects. Subject participation length is about 7 months with 6 scheduled study visits.

Methodology: After successfully completing the screening and qualification phase, participants will be randomized to treatment at Visit 1 for 5 cycles of double-blind treatment. Participants will be evaluated monthly during the randomization phase for adverse events, concurrent medication, and primary and secondary efficacy variables.

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• Drug: Fluoxetine
• Drug: Calcium
• Drug: Placebo

• Active Comparator: I: Active Comparator Fluoxetine
• Active Comparator: Calcium

Inclusion Criteria:

1. Menstruating
2. Meet criteria for moderate to severe PMS
3. Report PMS symptoms for at least 9 out of the 12 months prior to screening
4. Are using an adequate method of birth control.

Exclusion Criteria:

Any candidate who:

1. Fulfills MINI (DSM-IV) criteria for a serious AXIS 1 disorder
2. Fulfills DSM-IV criteria during the charting phase consistent with a diagnosis of psychotic disorder, bipolar disorder or major depressive disorder
3. Has a severe, co-existing condition that, in the investigator's opinion, renders the patient unsuitable for the study
4. Poses a significant risk of suicide
5. Takes ongoing medication that could treat PMS symptoms
6. Has a history of hypersensitivity or adverse reaction to fluoxetine or calcium
7. Is lactating, pregnant or is planning to become pregnant during the course of the study.