Causes of Hypothyroidism

Here we discuss the general causes of hypothyroidism

There are four basic reasons that a patient may have low thyroid function. Each of these disorders is directly related to malfunctions in the hypothalamic-pituitary-thyroid axis. Visit the Texas medical center endocrinologists at Houston Thyroid and Endocrine Specialists to review the proper thyroid diagnostic workup to determine what may be causing your low thyroid function.

The thyroid gland itself is not producing thyroid hormone.

This condition is called "primary hypothyroidism" and it accounts for 99% of all cases of hypothyroidism. Endocrinologists can differentiate among the many causes and each cause has different treatment options. The most common cause of primary hypothyroidism is Hashimoto's thyroiditis which is an autoimmune disease which runs in families. Yes, there is evidence that COVID SARS--CoV2 and the vaccines for COVID can cause hypothyroidism via an immune process. Several small studies (case reports) have shown SARS CoV-2 vaccines can trigger an autoimmune reaction in the thyroid of susceptible patients causing hyper and hypothyroidism. (1) Dr. Jogi says "COVID Vaccine induced Hashimoto's hypothyroidism should not be surprising since Hashimoto's is an autoimmune process and many autoimmune processes are though to begin with a viral infection."

The pituitary is not stimulating the thyroid gland to make thyroid hormone.

This is condition is called "secondary hypothyroidism". Most commonly this is due to pituitary damage from a brain tumor called a pituitary adenoma or previous brain radiation treatments. Rare examples from medications like bexarotene which have case reports.

The hypothalamus is not functioning properly.

This is very rare and usually discovered after a pituitary workup.

There is resistance to the action of thyroid hormone in the body.

This is extremely rare.


(1) J Endocrinol Invest. 2022; 45(12): 2283–2289 SARS-CoV-2 vaccine may trigger thyroid autoimmunity: real-life experience and review of the literature R. M. Ruggeri