Progesterone, like all hormones, needs to be in balance to ensure proper health. Progesterone is naturally produced during the second week of a woman's period, but her ovaries may produce it in excess. A woman's body produces progesterone to prepare the lining of the uterus to accept a fertilized egg. When no egg is fertilized, progestin levels fall and the lining is shed, which is what produces menstruation.
Progesterone is a member of a group of hormones known as progestogens or progestins (the exogenous or synthetic versions.) These can be found in birth-control pills, in hormones given during menopause for replacement therapy, or in medications to correct abnormal bleeding problems during menses. These hormones are also used to counteract PMS syndrome, infertility, and pregnancy loss. Many women are aware of the effects of too little or too much estrogen, but have never looked up progesterone side-effects.
Approximately 30-40% of menopausal women who take progesterone experience unpleasant PMS-like symptoms such as moodiness, irritably, and muscle aches. Individuals who have had significant premenstrual symptoms while they were premenopausal are more likely to be affected.
Progestins produce moodiness and irritability by affecting specific sites in the brain. Changing the type of progesterone, the dose, the route of administration and the length of treatment can lessen this effect.
One mysterious effect in the progesterone intolerant women is bladder problems. Some women have either a great increase in urinary tract infections or a feeling like they are having an infection as soon as they try taking a "normal" progesterone dose. If bladder symptoms start and stop with starting and stopping progesterone, they may be related.
Progesterone in high doses can cause side-effects. In one study, oral micronized progesterone at a dose of 400mg per day was associated with dizziness, abdominal cramping, headache, breast pain, muscle pain, irritability, nausea, fatigue, diarrhea and viral infections.[Medical Economics; 1999: p.125]