Certain personal circumstances, medical conditions and medications can adversely affect the performance of the Clearblue Easy Fertility Monitor. These include menopausal symptoms, breast feeding, impaired liver or kidney function, polycystic ovarian syndrome, antibiotics containing tetracycline (not oxytetracycline or doxycycline) and treatments that affect your cycle e.g. hormonal contraception, certain fertility treatments and hormone replacement therapy. Couples with medically diagnosed fertility problems should consult their physician before using this product.