Drug-induced hypothyroidism is an adverse reaction to the use of a medication that results in an underactive thyroid gland. Thyroxine (T4), a hormone the thyroid gland produces, regulates the heart rate, digestion, mental development, and physical growth. When not enough T4 is secreted, damage to tissues and organs in every part of the body can occur and other life-threatening complications can develop. Complications of drug-induced hypothyroidism include:
- Heart disease
- Miscarriage
- Infertility
- Pituitary tumors (extremely rare)
Myxadema, the most severe form of hypothyroidism is seldom drug-related. It also bears noting that too much iodine can cause hypothyroidism OR hyperthyroidism.
Symptoms of hypothyroidism range from mild to severe, and may include:
- Weakness, fatigue
- Cold intolerance
- Constipation
- Brittle fingernails
- Coarsening and thinning of hair
- Dry skin
- Cold and/or yellow tint to skin
- Memory problems
- Depression
Less common symptoms may include:
- Enlarged thyroid gland (goiter)
- Modest weight gain (usually less than 10 lbs.)
- Swelling of limbs, extremities and especially around the eyes
- Hoarseness
- Slowed speech
- Muscle aches and cramps
- Menstrual disorders
- Joint stiffness
Drugs that are associated with, or can cause hypothyroidism include:
- Lithium carbonate
- Dopamine
- Nitroprusside
- Perchlorate
- Amiodarone (such as Amiodarone, Pacerone, and Cordarone)
- Interferon alpha (such as Infergen, Wellferon, and Rebetron)
- Thalidomide
- Stavudine (Zerit)
- Povidone iodine (Betadine)
- Sulfonylureas
Drugs used to treat an overactive thyroid (hyperthyroidism) can also cause hypothyroidism. These include:
- Propylthiouracil (PTU)
- Potassium iodide
- Radioactive iodine
- Methimazole (Tapazole)
To diagnose drug-induced hypothyroidism, the patient’s medical history should be thoroughly reviewed. Vital signs (temperature, blood pressure, pulse, and rate of breathing) are checked for a slowed metabolism. A physical exam may reveal goiter and a chest x-ray may also reveal an enlarged heart. The blood is tested for levels of:
- T4 (free T4 test, which is not affected by protein levels)
- T3
- Thyroid stimulating hormone (TSH)
- Cholesterol
- Liver enzymes
- Serum prolactin
- Serum sodium
- Blood glucose
- Red blood cells (complete blood count)
The offending drug or agent should be discontinued, but not before first consulting with the healthcare provider. Withdrawal from some medications can result in serious or even life-threatening reactions if not done gradually. The medication may also need to be replaced.
The most commonly used medication to treat hypothyroidism is levothyroxine (also known as L-thyroxine), a synthetic thyroid replacement hormone. The purpose of the treatment, which is known as replacement therapy, is to return TSH to normal levels.
During replacement therapy, the patient should report any symptoms of increased thyroid activity such as rapid weight loss, sweating or restlessness. Early treatment usually results in recovery, but replacement therapy may need to be continued to avoid a return of the condition.
Drugs with a potential to cause hypothyroidism should be used with caution, and individuals who take them should be monitored periodically.