Hyperplasia, an abnormal thickening of the uterine lining, occurs when a woman produces the hormone estrogen without producing the hormone progesterone. To treat hyperplasia, progesterone supplements are given for several weeks and then withdrawn, which brings on a menstrual bleed. Natural progesterone comes in prescription pills, gels and vaginal creams as well as over-the-counter creams. Both prescription and over-the-counter supplements cause side effects. A study published in June 2005 in the "Journal of Clinical Pharmcology" found that over-the-counter Pro-gest was absorbed in the same quantities as prescription Prometrium, meaning the same side effects could occur.
Dizziness
One of the most common symptoms of natural progesterone in oral form is dizziness, which affects up to 24 percent of premenopausal women and 15 percent of postmenopausal women who take Prometrium, according to Drugs.com. Drowsiness, confusion and fainting when standing up from a sitting position can also occur. Fainting most often occurs when you first start taking the medication; get up slowly and sit for a few minutes before rising from a lying-down position, the National Institutes of Health recommends. Around 5 percent of women taking prescription vaginal gels or suppositories experience dizziness. Don't drive or operate machinery until you know how the drug affects you.
Cramping
Cramping and abdominal discomfort occur in 20 percent of premenopausal women taking natural progesterone supplements and in 12 percent of postmenopausal women, eMedTV reports. Abdominal pain may be accompanied by constipation in 27 percent of women and nausea in 22 percent of women using vaginal progesterone. Bloating can contribute to abdominal pain in 8 percent of women taking oral or vaginal supplements, Drugs.com reports.
Depression
Depression occurs in up to 29 percent of menopausal women, according to eMedTV and 19 percent of women overall according to Drugs.com. Anxiety, worry, forgetfulness and insomnia may also occur.
Headaches
Headaches affect up to 31 percent of postmenopausal women and 16 percent of premenopausal women taking natural progesterone supplements, eMedTV states.
Breast Pain
Breast pain or tenderness affects 27 percent of postmenopausal women and 16 percent of premenopausal women, according to eMedTV. Breast lumps requiring excisional biopsy occur in 2 percent of women; two percent of women also develop breast cancer while taking natural progesterone, Drugs.com warns.
