In the first place, women who are breastfeeding should not be taking oestrogen containing birth control pills or any other pills containing oestrogens, exactly because they may significantly decrease the milk supply. I think that fluconazole can decrease the milk supply even without the concomitant use of oestrogens. Its parent, ketoconazole, is known to have androgen like effects, or stimulate androgens, which might explain this. Usually it is not a problem, and usually, even if it is, the milk comes back pretty smartly after the course of treatment. Jack Newman, MD, FRCPC