Endocrine glands, and the hormones they secrete, significantly affect the central nervous system (CNS). Thyroid hormones in particular are crucial to the formation and function of the CNS. The inactive thyroid hormone T4 is secreted by the thyroid gland and transported across the blood-brain barrier, where it is converted into T3, the active thyroid hormone. Adequate thyroid hormone levels are necessary to support both the neurons, which are the structural and functional units of the nervous system, and the glia cells, which connect and support the brain and spinal cord.

Thyroid Dysfunction and Mental Illness

Thyroid abnormalities may lead to mental disorders such as:

• Anxiety
• Depression
• Bipolar disorder
• Schizophrenia

Hypothyroidism may contribute to:

• Apathy
• Low energy
• Impaired memory
• Problems with attention span
• Mood swings
• Impatience
• Irritability
• Mental decline in the elderly

Negative Effects of Antidepressants on Thyroid Function

To make matters worse, medications used to treat mental disorders may adversely affect thyroid function. In Clinical Neuropharmacology, a comprehensive review of the medical literature concluded that some medications that are use to treat bipolar disorder, schizophrenia, and depression are associated with thyroid function abnormalities. These include lithium, phenothiazines, and tricyclic antidepressants. Patients using these classes of medications should be monitored for thyroid dysfunction. Patients receiving other types of mental illness drug therapies may also need to be monitored.