Cold and flu remedies with antihistamines. Designed to dry up overactive mucous membranes in your nose and throat, these popular remedies also occasionally thicken or dry up cervical mucus. For sperm, that's tantamount to swimming across a bone-dry desert or through a sea of Jell-O.

Corticosteroids. Creams and ointments containing corticosteroids are used to relieve the redness, swelling, and itching of skin conditions, like psoriasis. These products can cause irregular menstrual periods, depending on the potency of the drug and the amount used.

High blood pressure medications. Potassium-sparing diuretics that contain spironolactone (such as Aldactone) can also throw off menstrual cycles.

Ibuprofen. Pain relievers, such as Advil or Aleve, sometimes sabotage ovulation, particularly if you're taking them regularly. "If you're on fertility medication or have been trying unsuccessfully to get pregnant, just stick with acetominophen (Tylenol)," Notes Mitchell N. Essig, MD, an obstetrics and gynecology instructor at Albert Einstein College of Medicine at Yeshiva University in the Bronx, who also has a private Manhattan practice in reproductive endocrinology and infertility.