How Taking Lithium May Affect Your Thyroid

This bipolar disorder treatment can influence thyroid hormones

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People with bipolar disorder, sometimes referred to as manic depression, are often surprised to learn that thyroid problems are a side effect of taking lithium, which is a medication used to treat this mental health condition. This can be a concern for those who already have been diagnosed with thyroid disease, as well as those who haven't—but now run the risk because of their lithium use.

Lithium has several biological effects on the thyroid, some of which include:

  • Increasing iodine content within the thyroid gland
  • Reducing your thyroid gland's ability to produce thyroxine (T4) and triiodothyronine (T3)
  • Blocking the release of thyroid hormones from the thyroid gland
  • Altering the structure of a protein in the thyroid gland, called thyroglobulin, which is involved in the making of thyroid hormone

Due to these effects and others, lithium may cause goiter (an enlarged thyroid), as well as hypothyroidism (an underactive thyroid). It is also linked to the development of hyperthyroidism (overactive thyroid) in some people, although this is rare. 

An Overview of Bipolar Disorder

Lithium and Goiter

Goiter, the term for an enlarged and swollen thyroid gland, is the most common thyroid-related side effect of lithium, occurring in approximately 40 percent to 50 percent of all patients. Goiter usually develops within the first two years of lithium treatment and causes a thyroid gland that is approximately twice the normal size.

Goiter formation is believed to occur as a result of lithium-induced changes in the function of certain hormones and molecules, including insulin-like growth factor and tyrosine kinase.

Treatment with thyroid hormone replacement medication (levothyroxine) may be used to decrease the size of the goiter; surgery is needed if the goiter becomes too large and narrows the airway.

Lithium and Hypothyroidism

Hypothyroidism is estimated to occur in about 20 percent to 30 percent of all patients taking lithium. It is most common in women over the age of 45 and in people with a family history of thyroid disease. As with goiter, hypothyroidism generally develops within the first two years of lithium treatment.

Hypothyroidism from lithium use can occur in the presence or absence of a goiter and is usually subclinical, meaning a person has an elevated thyroid stimulating hormone (TSH) level but normal T4 and T3 levels. A small percentage of patients, however, will develop overt hypothyroidism from lithium therapy, with its typical signs and symptoms.

Treatment of subclinical or overt lithium-induced hypothyroidism entails taking thyroid hormone replacement medication.

Thyroid Goiter and Thyroid Nodules

Lithium and Hyperthyroidism

Lithium treatment also appears to be linked to an increased risk of hyperthyroidism, although this is not as common as goiter or hypothyroidism. It's not completely clear how hyperthyroidism develops with lithium therapy. It's possible that transient hyperthyroidism may be from the direct toxic effect of lithium on the thyroid gland. Lithium may also induce thyroid inflammation, as evidenced by the production of thyroid auto-antibodies in some people.

Treatment of lithium-induced hyperthyroidism involves taking an anti-thyroid drug. If a person develops lithium-induced Graves' disease (autoimmune hyperthyroidism), treatment with radioactive iodine or surgical removal of the thyroid may be necessary.

Benefits vs. Risks

Lithium is often critical in the management of bipolar disorder, so the risk of developing thyroid problems should not rule out the use of this medication. It is important, however, to see your doctor regularly for thyroid function testing and report any new symptoms right away.

Diagnosing Lithium-Induced Thyroid Dysfunction

Before you are prescribed lithium, your doctor should perform the following standard tests used to diagnose thyroid dysfunction.

Clinical Examination

Your doctor will ask about your symptoms and perform several other clinical assessments. Tests include:

  • Palpating your neck and feeling for enlargement, lumps, or irregularity in the shape of your thyroid
  • Testing your reflexes: A hyper-response may be indicative of an overactive thyroid, and a blunted reflex response is often associated with hypothyroidism.
  • Checking your heart rate, rhythm, and blood pressure. Lower heart rate and/or blood pressure can be associated with an underactive thyroid; elevated heart rate and/or blood pressure are commonly linked to hyperthyroidism.
  • Weighing you: Unexpected weight gain is often linked to hypothyroidism, while weight loss is linked to hyperthyroidism.
  • Examining your eyes, looking for classic thyroid signs, including bulging of eyes, a prominent stare, and dry eyes
  • Observing the general quantity and quality of your hair, skin, and nails: Changes in texture can indicate hyperthyroidism and hypothyroidism.

Blood Tests

Thyroid blood tests are used to measure levels of these substances:

  • Thyroid stimulating hormone (TSH)
  • Total T4/total thyroxine
  • Free T4/free thyroxine
  • Total T3/total triiodothyronine
  • Free T3/free triiodothyronine
  • Reverse T3
  • Thyroglobulin/thyroid binding globulin/TBG
  • Thyroid peroxidase antibodies (TPOAb)/antithyroid peroxidase antibodies
  • Thyroglobulin antibodies/antithyroglobulin antibodies
  • Thyroid receptor antibodies (TRAb)
  • Thyroid-stimulating immunoglobulins (TSI)
Understanding Thyroid Function Tests and Normal Ranges

Radioactive Iodine Uptake Test

By measuring the amount of iodine that is taken up by the thyroid gland, doctors may determine whether the gland is functioning normally. A very high radioactive uptake (RAIU) is seen in people with hyperthyroidism, while a low RAIU is seen in those with hypothyroidism.

In addition to the radioactive iodine uptake, a thyroid scan may be obtained, which shows a picture of the thyroid gland.

If you are taking lithium, your doctor should reevaluate your thyroid function using these same tests every six to 12 months—sooner if you begin to show symptoms that suggest you have thyroid dysfunction.

If thyroid dysfunction occurs while on lithium, treatment of the underlying thyroid problem is warranted, but discontinuation of lithium is not generally necessary. Instead, your psychiatrist will continue to manage your lithium and bipolar disease, and your primary care physician or endocrinologist (a doctor who specializes in thyroid diseases) will manage and treat your thyroid problem. 

A Word From Verywell

The link between lithium use and thyroid dysfunction, especially goiter and hypothyroidism, is well-known, but don't be scared off from taking lithium for your bipolar disease because of this potential side effect. Lithium-induced thyroid problems can be easily detected and effectively treated.

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