Low TSH (Thyroid Stimulating Hormone) Symptoms and Treatment

Low thyroid stimulating hormone (TSH) levels often occur with hyperthyroidism (overactive thyroid). However, a low TSH test result needs to be evaluated in the context of other thyroid tests and your individual symptoms and health history.

Several conditions can include low TSH levels and hyperthyroidism, including Graves' disease and thyroid nodules. About 1% of adults in the United States have hyperthyroidism.

This article explains TSH levels, why a low TSH might occur, and any low TSH symptoms (though not everyone has them). It also discusses possible causes of low TSH and how it's treated.

What Is Low TSH?

Thyroid stimulating hormone (TSH) is produced and released by the pituitary gland, found at the base of your brain. It acts as a messenger to the thyroid gland to produce thyroid hormone T4 (thyroxine), which converts to T3 (triiodothyronine) in the body.

The release of TSH is based on how much T4 the pituitary gland recognizes in the bloodstream, where it (as well as T3) is carried by specific transport proteins. Low TSH can arise because:

• The thyroid is producing too much hormone (hyperthyroidism).
• The pituitary gland isn't functioning well and fails to tell the thyroid to produce hormones.
• The transport proteins are affected by another condition (like pregnancy).

A combination of TSH level and other thyroid hormone results are needed for diagnosis. For example, circulating T3 increases before T4 in people with hyperthyroidism. The values of these other tests, along with TSH level, are key to understanding and treating the cause.

Symptoms of Low TSH

Though TSH levels are important measures of thyroid function, low TSH levels do not always cause symptoms. However, low TSH symptoms often are associated with hyperthyroidism, which can cause:

• Irritability
• Feeling tired
• Muscle weakness
• Trouble tolerating heat
• Difficulty sleeping
• Tremors
• Rapid and irregular heartbeat
• Diarrhea
• Weight loss
• Mood swings

Although less common, some rare symptoms of low TSH levels linked to hyperthyroidism include: 

• Heart arrhythmias such as atrial fibrillation
• High fever 
• Mental status changes

Other medical problems, like anemia (a decrease in red blood cells), can also indicate that someone has low TSH and hyperthyroidism.

Causes of Low TSH

A low TSH level of less than 0.4 mU/L can be due to several causes, including:

• Hyperthyroidism due to autoimmune disorders (like Graves' disease) or thyroid gland changes (like nodules)
• Pituitary gland function
• Too much thyroid medication in people treated for hypothyroidism
• Levels of other hormones (for example, an estrogen drop at menopause)

Pregnancy is a common cause of lower TSH levels and associated hyperthyroidism.

Pregnancy Concerns

Mild hyperthyroidism while pregnant does not always cause problems. Moderate-to-severe hyperthyroidism can lead to various complications. 

• For the baby: Uncontrolled or untreated hyperthyroidism of the mother during pregnancy is associated with a baby size that is small for gestational age, preterm birth, stillbirth, and possibly congenital malformations. 
• For the mother: Potential complications of untreated hyperthyroidism include preeclampsia and, rarely, thyroid storm. 

Though uncommon, hyperthyroidism may also occur in mothers of newborns with a history of treated Graves' disease (meaning their disease is in remission). Thus, it's important to notify your healthcare provider of any history of thyroid disease in addition to active thyroid disease.

Complications of Low TSH

Low TSH levels are an indicator of abnormal thyroid function and should be corrected.

The thyroid plays a central role in numerous body processes, such as energy, metabolism, skin health, mood, and heart function. Over the long term, low TSH levels can potentially lead to damage to major organ systems, so they should not be dismissed. 

Serious complications can include:

• Eye disease called Graves' ophthalmopathy
• Osteoporosis or bone loss
• Infertility
• Heart problems
• Heart arrhythmias leading to stroke or heart failure

When to See a Healthcare Provider

A low TSH level is not often a medical emergency. If you have blood work that illustrates a low TSH level, talk with your healthcare provider about the potential causes and the next steps for diagnosis and treatment.

Fortunately, there are numerous treatments available for low TSH levels, including medications and procedures. If you experience any severe symptoms, such as high fever, palpitations, or changes in thinking or memory, seek care immediately. 

Treatment for Low TSH

The treatment for low TSH levels will depend on the underlying cause. In many cases, low TSH results are associated with hyperthyroidism that can be treated with:

• Medications including beta blockers and antithyroid drug Tapazole (methimazole)
• Radioiodine therapy (capsules taken by mouth), but with the eventual risk of hypothyroidism
• Thyroid surgery (for example, to remove a large goiter)

Summary

A low TSH level is linked to thyroid hormone levels in the body and is a common condition. In some cases, increased levels of thyroid hormone caused by supplementation or conditions such as Graves' disease can contribute to a low TSH. 

The diagnosis and treatment will depend on your TSH level along with the results of other thyroid function tests, as well as other tests your healthcare provider finds necessary when considering your medical history and evaluating any symptoms.