You should not take Arimidex if you are breastfeeding, pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Arimidex may cause damage to developing embryos. You should use an effective non-hormonal type of birth control -- such as condoms, a diaphragm along with spermicide, or a non-hormonal . – while you are taking Arimidex. Ask your doctor which type of non-hormonal birth control would be best for you, as well as how long you should use this type of birth control after you stop taking Arimidex.
A number of investigators have reported on a rather rare syndrome of excess aromatase activity. In boys, it can lead to gynecomastia , and in girls to precocious puberty and gigantomastia . In both sexes, early epiphyseal closure leads to short stature. This condition is due to mutations in the CYP19A1 gene which encodes aromatase.  It is inherited in an autosomal dominant fashion.  It has been suggested that the pharaoh Akhenaten and other members of his family may have suffered from this disorder,  but more recent genetic tests suggest otherwise.  It is one of the causes of familial precocious puberty—a condition first described in 1937. 
For most post-menopausal women whose cancers are hormone receptor-positive, most doctors recommend taking an AI at some point during adjuvant therapy. Right now, standard treatment is to take these drugs for about 5 years,or to alternate with tamoxifen for a total of at least 5 years, or to take in sequence with tamoxifen for at least 3 years. Studies are now being done to see if taking an AI for more than 5 years would be more helpful. Tamoxifen is an option for some women who cannot take an AI. Taking Tamoxifen for 10 years is considered more effective than taking it for 5 years, but you and your doctor will decide the best schedule of treatment for you.