Blood

• According to the National Cancer Institute, tamoxifen increases the risk of blood clots. Clots may cause deep vein thrombosis in which clots lodge in veins, usually in the legs or groin area, causing a decrease in blood flow, vessel damage and inflammation. The clot may enlarge, and some clots may break loose, traveling through the blood to other parts of the body, such as the lungs or the brain, where a clot can block an artery and cause a stroke.
  
  "Lippincott's Nursing Drug Guide" notes that tamoxifen may also cause hypercalcemia (an increase in calcium in the blood) and a decrease in platelets, which increases risk of bleeding, so tamoxifen should not be taken with blood thinners, such as Coumadin. Tamoxifen may depress the bone marrow and interfere with production of red blood cells, leading to anemia, and white blood cells, interfering with the immune response and increasing risk of infection.
  
  

Gynecological/Genitourinary

• Tamoxifen increases risks of secondary cancers developing in the uterus, including endometrial cancer of the lining and sarcoma of the muscle. Women developing uterine cancer may experience vaginal bleeding and pain in the lower abdomen. Additionally, according to RxList, women may have symptoms associated with menopause, such as hot flashes, vaginal dryness and irregular periods, because of the antiestrogen effect of the drug, although the drug does not trigger actual menopause as the ovaries continue to produce estrogen in premenopausal women.
  
  Males taking tamoxifen may experience a decrease in libido and impotence.
  
  

Gastrointestinal

• As with many chemotherapeutic drugs, tamoxifen may cause nausea and vomiting and may alter the sense of taste, and this combination of side effects often results in weight loss during treatment. Some people may have diarrhea while others have constipation.
  
  

Central Nervous System

• Tamoxifen can cause headaches and dizziness. Some people have trouble sleeping and have increased anxiety, while others may develop clinical depression while taking the medication.
  
  

Musculoskeletal

• Generalized pain in bones, joints and muscles may occur as well as increased pain in the area of the tumor. Sometimes, a generalized rash occurs. Some people develop fluid retention and swelling of the lower legs and feet, increasing discomfort.
  
  

Eyes

• Tamoxifen can affect the eyes, resulting in decreased opacity (clearness) of the cornea, increased risk of retinopathy and decreased visual acuity, so frequent eye exams are necessary during treatment.
  
  

Warning

• Tamoxifen should not be taken with grapefruit as grapefruit interferes with metabolism (breakdown) of the drug and increases toxic effects. Tamoxifen should not be taken during pregnancy as it can cause serious damage to the fetus, so those of child-bearing age should practice birth control while taking the medication. Additionally, tamoxifen crosses into breast milk, so women should not breast-feed while taking tamoxifen.