Effects of Progesterone
Low progesterone is associated with numerous breast problems, including fibrocystic breasts
The study included 37 patients classified into mastalgia, fibrosis, fibrocystic disease, and fibroadenoma groups and 19 healthy age-matched volunteer women. In all patient groups, progesterone levels were significantly decreased. There was also an increased frequency of patients with low levels of estradiol (< 50 pg/ml). On the other hand, LH levels in fibrocystic disease and fibroadenoma groups were significantly increased.
http://www.ncbi.nlm.nih.gov/pubmed/9476089
PCOS is linked to low progesterone levels
PCOS is associated with decreased SHBG and progesterone.
http://www.diagnose-me.com/cond/C486172.html
Progesterone deficiency is secondary to impaired ovulation
Women with PCOS frequently have low progesterone levels. The best solution is to strengthen ovulation, as opposed to progesterone supplementation alone without investigating follicle development through ultrasound monitoring and estradiol levels.
http://www.inciid.org/faq.php?cat=infertility101&id=2
Progesterone causes insulin resistance
There is an increased insulin-resistant state during pregnancy mediated by the placental anti-insulin hormones estrogen, progesterone, human somatomammotropin; the pituitary hormone prolactin; and the adrenal hormone, cortisol.
http://www.ncbi.nlm.nih.gov/pubmed/8632110