One of the many actions of the "SSRI" (such as fluoxetine, Prozac), which aren’t related to their effect on serotonin, is to increase the concentration of allopregnanolone in the brain, imitating the action of increased progesterone. Following this discovery, Lilly got Prozac approved as a treatment for premenstrual syndrome. Since the production of allopregnanolone and progesterone depends on the availability of pregnenolone and cholesterol, a low cholesterol level would be one of the factors making this an inappropriate way to treat PMS. -Ray Peat