The ingredient anastrozole is present in anastrozole pills. Anastrozole is an aromatase inhibitor. For adjuvant therapy, anastrozole pills are often recommended in doses of 1 mg to postmenopausal women who have early, hormone receptor-positive breast cancer and is also used with other treatments such as surgery or radiation to treat breast cancer in women who have attained menopause. Some common side effects of Anastrozole 1mg tablets include headache, nausea, weakness, diarrhea, joint pain, muscle pain, and Rash.