Hypothyroidism - Resources

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Problems with Levothyroxine Treatment

Because levothyroxine is identical to the thyroxine the body manufactures, side effects are rare. Over- or under-dosing, however, is fairly common, although rarely serious in the short term.

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No Symptom Improvement When Normal Thyroid Levels Are Reached. Some patients fail to feel significantly better even when their thyroid levels become normal after taking thyroid replacement.

Some patients with persistent symptoms may benefit from triiodothyronine (T3), the other important thyroid hormone. In such cases, either a combination of a lower-dose of thyroxine with a small amount of T3 or natural dried thyroid hormone, which contains T3, may be helpful.

Side Effects of Overdosing. Overdosing can cause symptoms of hyperthyroidism. A patient with too much thyroid hormone in the blood is at an increased risk for abnormal heart rhythms, rapid heartbeat, heart failure, and possibly a heart attack if the patient has underlying heart disease. Excess thyroid hormone is particularly dangerous in newborns, and their drug levels must be carefully monitored to avoid brain damage.

Side Effects of Long-Term Treatment. Patients with hypothyroidism usually receive lifelong levothyroxine therapy. There has been some concern that long-term use will increase the risk of osteoporosis, as suppression therapy does. Studies indicate that postmenopausal women who are taking long-term replacement thyroxine at the appropriate dosage have no significantly increased risk for osteoporosis.

Drug Interactions with Levothyroxine. Many drugs interact with levothyroxine and may either enhance or interfere with its absorption. These drugs include: