Estrogen Side Effects in Dogs

Estrogen is a primary female sex hormone in dogs. It develops and maintains the female reproductive organs and secondary sexual characteristics. Veterinarians use estrogen therapy -- the administration of synthetic estrogen, or diethylstilbestrol -- to treat specific problems, such as urinary incontinence or involuntary urine leakage and some cancers. Although estrogen therapy is useful in these situations, it can cause various short- and long-term side effects, some of which are severe.

  1. Bone Marrow Suppression

    • In excessive doses, estrogen can depress bone marrow volume and reduce blood cell production. This interferes with immunity by lowering the white blood cell count; interferes with blood clotting by decreasing platelet formation; and can cause anemia by reducing the number of red blood cells. These effects can be irreversible and fatal.

    Aplastic Anemia

    • Anemia caused by bone marrow reduction and inability to make new red blood cells is called aplastic anemia. Symptoms in dogs include fever, recurrent infections, weakness and lethargy.

    Pyometra

    • High-dose estrogen therapy can increase the risk of the uterine infection pyometra in unspayed dogs. Symptoms include an elevated white blood cell count, vaginal discharge, and pus within the uterus. Risks include fatal uterine rupture and sepsis.

    Ovarian Tumors

    • High-dose estrogen therapy increases the risk of ovarian cancer in unspayed dogs. Symptoms of cancer on or in the ovaries include abdominal swelling, fluid within the abdominal cavity, loss of appetite, fever and lethargy.

    Polydipsia and Polyuria

    • Excessive thirst is called polydipsia. The normal intake of water for dogs is 20 to 40 milliliters per day per pound of body weight. More than this may be diagnosed as polydipsia. Excessive thirst can lead to excessive urination, or polyuria. Both are possible side effects of estrogen therapy at any dose.

    Short-term Effects

    • Side effects and their severity vary with the individual dog and the dosage of estrogen. Short-term side effects may include vomiting, vaginal bleeding, lethargy, diarrhea and loss of appetite. Dogs can also experience allergic reactions to estrogen medication. Signs of an allergic reaction include facial swelling, hives, scratching, sudden diarrhea or vomiting, seizures, pale
      gums and cold limbs. Allergic reactions require immediate veterinary care.