Low TSH: Symptoms, Causes & Treatment

Low TSH (thyroid-stimulating hormone) levels in the blood can be caused by Graves’ disease, thyroid nodules that produce hormones, thyroid inflammation (thyroiditis), use of certain medications, or, in rare cases, tumors that affect hormone production by the pituitary gland.

TSH levels are usually low when thyroid hormones T3 and T4 are high. The main symptoms of low TSH may include weight loss, tremors, or diarrhea, among others.

If a blood test shows low TSH, it is important to consult an endocrinologist or a primary care provider in order to identify the cause and begin the most appropriate treatment.

Main symptoms

The most common symptoms of low TSH include:

• Weight loss;

• Excessive sweating;

• Tremors;

• Heat intolerance;

• Diarrhea;

• Difficulty sleeping.

These symptoms usually appear when thyroid problems lead to an overproduction of thyroid hormones, a condition known as hyperthyroidism. In these cases, it is common for TSH levels in the blood to be low.

Does low TSH cause weight gain?

Hyperthyroidism generally leads to weight loss because it increases the body’s basal metabolic rate due to excessive production of thyroid hormones.

Confirming a diagnosis

A diagnosis of low TSH is confirmed by an endocrinologist or a primary care provider through a blood test that measures thyroid hormones, including TSH, free T4, and total T3.

In cases of hyperthyroidism, TSH levels are below the reference range (usually less than 0.4 mU/L in adults), while free T4 and total T3 may be normal or elevated.

Possible causes

The main causes of low TSH include:

• Graves’ disease;

• Thyroid nodules that produce T3 and/or T4;

• Use of certain medications, such as lithium or amiodarone;

• Tumors, especially those affecting the pituitary gland or hypothalamus;

• Thyroiditis (inflammation of the thyroid gland).

Low TSH usually indicates that the thyroid gland is producing too much hormone, but it can also result from a problem in the pituitary gland or hypothalamus, which are parts of the brain responsible for regulating TSH production.

Treatment options

Treatment for low TSH depends on the underlying cause. In cases of hyperthyroidism, treatment may involve:

• Antithyroid medications such as methimazole or propylthiouracil;

• Radioactive iodine therapy;

• Adjusting the dosage of medications that affect thyroid function;

• Thyroid surgery (thyroidectomy) to remove part or all of the gland.