Perimenopausal symptoms are similar to PMS and the reason for these symptoms may be the same. It is usually caused by insufficient progesterone because ovulation is sporadic. Women start to run out of eggs in their 30's. The peri menopausal period can start as early as the mid thirties or 40's and go on for 10 or more years. The antidote to the symptoms caused by estrogen dominance is natural hormone replacement therapy with bioidentical progesterone.