Symptoms of hypothyroidism (low levels of thyroid hormone) include fatigue, cold and heat intolerance, hypotension, fluid retention, dry skin and/or hair, constipation, headaches, low sexual desire, infertility, irregular menstrual periods, aching muscles and joints, depression, anxiety, slowed metabolism and decreased heart rate, memory impairment, enlarged tongue, deep voice, swollen neck, PMS, weight gain, hypoglycemia, and high cholesterol and triglycerides. Yet, more than half of all people with thyroid disease are unaware of their condition. Although both T4 (thyroxine, an inactive form that is converted to T3 in other areas of the body) and T3 (triiodothyronine, the active form) are secreted by the normal thyroid gland, many hypothyroid patients are treated only with levothyroxine (synthetic T4). Some hypothyroid patients remain symptomatic, and T3 may also be required for optimal thyroid replacement therapy. However, the only commercially available form of T3 is synthetic liothyronine sodium in an immediate release formulation which is rapidly absorbed, and may result in higher than normal T3 concentrations throughout the body causing serious side effects, including heart palpitations. Research indicates there is a need for sustained-release T3 preparations in order to avoid adverse effects.