Converting hypothyroidism to the euthyroid state with levothyroxine may increase the blood level of theophylline (Slo-Bid), and it may be necessary to change the dose of theophylline.

Taking levothyroxine at the same time as cholestyramine (Questran) or colestipol (Colestid), two cholesterol-lowering drugs, may decrease the effect of levothyroxine and lead to hypothyroidism. This occurs because the levothyroxine binds to the cholesterol-lowering drugs and is not absorbed. Taking the levothyroxine one hour before or four hours after cholestyramine or colestipol is necessary to prevent the binding.

PREGNANCY: Thyroid hormone therapy during pregnancy is usually safe but should be supervised by a physician.

NURSING MOTHERS: Thyroid hormone therapy in nursing mothers is usually safe but should be supervised by a physician.

SIDE EFFECTS: Levothyroxine therapy is usually well-tolerated. If symptoms occur, often they are due to toxic levels of thyroid hormone and the symptoms are those of hyperthyroidism. Symptoms may include all or some of the following: chest pain, increased heart rate or pulse rate, excessive sweating, heat intolerance, nervousness, headache, insomnia, diarrhea, vomiting, weight loss, or fever. Women may experience irregular menstrual cycles.

Reference: FDA Prescribing Information

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