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We know that the thyroid gland plays a significant role in nearly every function and system of the body, including the digestive, cardiovascular, musculoskeletal, and nervous systems. Studies have shown that thyroid hormone levels can also affect behavior, mood, and mental health. For example, hyperthyroidism -- an overactive thyroid -- is associated with symptoms of anxiety and panic disorder, while hypothyroidism -- an underactive thyroid -- can cause symptoms of depression and bipolar disorder.

How are hypothyroidism and bipolar disorder treated? Are they treated in tandem or as two separate disorders? Let’s dive in.

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Formerly called manic depressive illness or bipolar depression, bipolar disorder is a mental illness that causes shifts in mood, energy, weight, activity levels, concentration, and the ability to handle daily tasks. It affects men and women equally; 2.8% of the U.S. population is diagnosed with bipolar disorder, and nearly 83% of those cases are classified as severe.

The key types of bipolar disorder include the following:

Bipolar I Disorder: this type of disorder involves manic episodes that can last up to a week, and in some cases, it requires hospitalization to help minimize symptoms

Bipolar II Disorder: less severe than type 1, this is defined as having a unique pattern of depressive episodes and hypomanic episodes

Cyclothymic disorder: the least severe form, which involves recurrent hypomanic and depressive symptoms that are neither long-lasting nor highly intense. These symptoms do not qualify this disorder type to be considered as hypomanic or depressive episodes, compared to type 2

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The most common drug used for bipolar disorder, especially for the past 70 years, is lithium. Lithium treatment aims to prevent relapses and treat related conditions such as mania and depression. The efficacy of lithium as a treatment for bipolar has been shown, including groups such as pediatric patients, geriatric patients, and pregnant and postpartum patients. A subset of patients has lithium-resistant bipolar illness. In those cases, other pharmacologic treatments, including antidepressant therapy and antipsychotic medications, have been shown to have beneficial effects in regulating mood and reducing the frequency and severity of manic and depressive episodes.

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Having bipolar disorder, and treating it with lithium, are both associated with thyroid disorders. A study from 2021 reported that people with bipolar disorder experience significant changes in their thyroid hormone levels during a depressive or hypomanic episode. Each patient in the study had blood samples collected to measure thyroid hormone levels and depressive and manic symptoms, assessed by two different scales (MADRS & YMRS). The study found that Free T3 (free triiodothyronine) levels (T3 is the active form of thyroid hormone) were significantly different in patients experiencing manic episodes and those experiencing depressive episodes. The thyroid axis dysfunction was also far more severe for people experiencing manic episodes.

Lithium therapy is a well-known trigger of autoimmunity, leading to the onset of drug-induced hypothyroidism. In fact, some studies show that up to 50% of patients treated with therapeutic doses of lithium will develop an underactive thyroid. Lithium-induced hyperthyroidism and Graves’ disease are less common but can also occur.

In addition to the use of lithium, other antipsychotic drugs and tricyclic antidepressant medication can interfere with both thyroid hormone production and TSH levels.

Experts recommend that patients with bipolar disorder being treated with lithium, antipsychotic drugs, or tricyclic antidepressants should have frequent thyroid blood testing done to monitor for any thyroid changes. This is in addition to monitoring for common symptoms of hypothyroidism.

It can be confusing, however, as some symptoms of hypothyroidism cross over to symptoms of bipolar disorder, including weight changes, fatigue, difficulty concentrating, and mood changes.
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In some situations, lithium or antidepressants aren’t an option or effective enough at resolving bipolar depression. Studies have shown success in using levothyroxine thyroid hormone treatment to manage both treatment resistant bipolar disorder and hypothyroidism concurrently.

There is also some evidence favoring the use of thyroid hormone replacement therapy as an adjunctive treatment to help stabilize mood in patients with more chronic and severe bipolar disorder.

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There’s no reason you can’t live a healthy and vital life with bipolar disorder and hypothyroidism. The keys are knowledge, careful management, and the right treatments.

If you have bipolar disorder, it’s crucial to test your thyroid levels frequently. The convenient Paloma Complete Thyroid Test Kit can make it easy, private, and affordable to test your Thyroid Stimulating Hormone (TSH), Free Thyroxine (Free T4), Free Triiodothyronine (Free T3), and Thyroid Peroxidase Antibodies (TPOAb). To diagnose, treat, and manage your hypothyroidism, you can schedule a virtual visit with one of our thyroid-savvy Paloma doctors. Paloma’s practitioners can work with you to monitor your thyroid levels regularly, assess any symptoms and clinical manifestations of hypothyroidism, and prescribe appropriate treatment for your underactive thyroid condition as necessary.