Section 3.6.1

Thyroid Hormones

General Description

Thyroid hormones are used in psychiatry as adjuvants to antidepressants, often in an attempt to convert an antidepressant-nonresponsive patient to an antidepressant-responsive patient. In the United States, the two most commonly used thyroid hormones are L-triiodothyronine and T4(levothyroxine). In the body, exogenous thyroxine is converted into triiodothyronine.

Indications for Medication

The major indication for thyroid hormones in psychiatry is an adjuvant to antidepressants. There is no correlation between the laboratory measures of thyroid function and the response to thyroid hormone supplementation of antidepressants.

If the patient has not been responsive to a six-week course of antidepressants at appropriate dosages, adjuvant therapy with lithium or a thyroid hormone is a good alternative. Most clinicians use adjuvant lithium before trying a thyroid hormone.

Clinical Guidelines

The available clinical data suggests that T3(liothyramine) or L-triiodothyronine is more effective than T4(levothyroxine). Several studies have indicated the use of L-triiodothyronine converts 33-75% of antidepressant non-responders to responders, these figures are still controversial. More research studies need to verify the real efficacy of thyroid hormone supplementation.

The daily dosage is 5-25 of L-triiodothyronine or 25-75 mcg of T4(levothyroxine) added to the patient's regular antidepressant regimen. L-triiodothyronine has been used as a successful adjuvant for all available antidepressant drugs. Clinical data regarding its use with the newer antidepressants (like bupropion or fluoxetine) is unfortunately limited.

An adequate trial of L-triiodothyronine supplementation should last 7-14 days. If the patient responds to L-triiodothyronine supplementation, the drug may be continued for a longer period of time. Monitoring of Thyroid Function tests is appropriate in this situation.

Adverse Effects

Thyroid hormones should be administered with caution to patients with cardiac disease, angina, or hypertension. The hormones are contraindicated in thyrotoxicosis and uncorrected adrenal insufficiency and in patients with acute myocardial infarctions.

The common adverse effects associated with thyroid hormone supplementation are weight loss, palpitations, nervousness, diarrhea, abdominal cramps, sweating, tachycardia, increased pulse, increased blood pressure, tremors, headache and insomnia.

Thyroid hormones can be administered safely to pregnant women because the thyroid hormones do not cross the placenta. Thyroid hormones are minimally excreted in the breast milk, and thyroid hormones have not been shown to cause problems in nursing babies.

Drug-Drug Interactions

Thyroid hormones can potentiate the effects of warfarin and other anticoagulants by increasing catabolism of clotting factors. Thyroid hormones can increase the insulin requirement for diabetic patients. Sympathomimetics and thyroid hormones should be used with caution because of the risk of cardiac decompensation.

The consent form for this medication is "Non-psychoactive Medications for Psychiatric Conditions."