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Can low TSH cause fatigue?

Thyroid stimulating hormone (TSH) is a hormone produced by the pituitary gland that regulates the production of thyroid hormones T3 and T4. TSH levels outside the normal range, whether too high or too low, can cause symptoms like fatigue due to the dysregulation of metabolism. This article will examine whether low TSH levels specifically can be a cause of fatigue.

What is TSH?

TSH stands for thyroid stimulating hormone. It is produced by the pituitary gland and acts on the thyroid to stimulate the production and release of thyroid hormones T3 (triiodothyronine) and T4 (thyroxine).

TSH is regulated through a negative feedback loop. When T3 and T4 levels in the blood are low, the pituitary gland is stimulated to release more TSH. This in turn tells the thyroid gland to produce more T3 and T4. When T3 and T4 levels are high enough, this signal is stopped through the feedback inhibition of TSH production.

Normal TSH levels can vary slightly between labs, but generally fall in the range of 0.4-4.0 mIU/L. Abnormal TSH levels outside this reference range can indicate thyroid dysfunction.

What causes low TSH?

There are several potential causes of a low TSH level:


Hyperthyroidism, or an overactive thyroid, is one of the most common causes of a suppressed TSH level. With too much thyroid hormone circulating in the bloodstream, the negative feedback loop tells the pituitary gland to stop producing TSH.

Graves’ disease is the most common cause of hyperthyroidism. It causes the thyroid gland to become enlarged and overproduce thyroid hormones. Other causes include thyroid nodules or thyroiditis (inflammation of the thyroid).

Non-thyroidal illness

Serious illness not originating from the thyroid can also suppress TSH levels. This is sometimes referred to as “euthyroid sick syndrome.” Diseases like diabetes, liver failure, or a major infection can disable the pituitary’s ability to make enough TSH.


Certain medications can influence thyroid function and lower TSH. Steroids like prednisone, dopamine agonists, and high doses of aspirin or its derivatives may lower TSH.

Pituitary disorders

Since the pituitary gland produces TSH, disorders involving the pituitary can affect TSH levels. For example, a pituitary tumor may disrupt TSH production and cause low levels.

Resistance to TSH

In rare cases, tissues can become resistant to TSH. Even though TSH levels are normal or elevated, the thyroid gland does not respond as expected. This leads to dysfunction in regulating thyroid hormones.

Symptoms of low TSH

What symptoms could low TSH levels potentially cause? The primary symptoms originate from too much thyroid hormone, or hyperthyroidism.

Common symptoms may include:

– Fatigue
– Weight loss
– Increased appetite
– Anxiety or nervousness
– Sweating
– Difficulty tolerating heat
– Restlessness
– Fast heart rate (tachycardia)
– Irregular heartbeat (arrhythmias)
– High blood pressure
– Muscle weakness
– Trembling hands
– Diarrhea
– More frequent bowel movements

Since TSH helps regulate the body’s metabolism, disruption of its function through low levels affects many different systems. However, symptoms can vary substantially depending on the underlying cause and severity of the hormone imbalance.

Can low TSH cause fatigue?

Yes, low TSH levels can often cause fatigue. Let’s examine the reasons why.

With low TSH, the main mechanism causing fatigue stems from elevated thyroid hormone levels. Excess T3 and T4 speed up cellular processes and place higher demands on the body. This creates a hypermetabolic state.

Some key ways this leads to fatigue include:

Faster metabolism, more calories burned

The body has to work harder just to maintain its basal metabolic rate. More calories are burned at rest. This increased workload can lead to exhaustion faster.

Poor sleep

The increased metabolism makes it harder to fall and stay asleep. Disrupted sleep directly worsens fatigue.

Nutrient depletion

All the extra energy expenditure can burn through nutrients more quickly. Deficiencies in iron, B12, and other nutrients hamper energy production.

Impaired muscle function

Excess thyroid hormones cause muscles to break down faster. This loss of proteins and impaired muscle performance contributes to weakness and fatigue.

Stress hormones

The excess thyroid hormone also causes secretion of adrenaline and cortisol. These stress hormones help mobilize energy in the moment, but when chronically elevated can worsen fatigue.

Heart effects

Palpitations, racing heart, and high blood pressure caused by low TSH increase demands on the cardiovascular system. This strains the body’s energy reserves.

So in summary, the change in metabolism and cascade of effects stemming from hyperthyroidism are the reasons low TSH often causes fatigue. Treating the hormone imbalance can help resolve these issues.

Who is most at risk for fatigue from low TSH?

Those most likely to experience significant fatigue from low TSH include:

– People with hyperthyroidism – Grave’s disease, thyroiditis. The lower the TSH, typically the worse hyperthyroid symptoms like fatigue will be.

– Those with severe non-thyroid illness that suppresses TSH substantially.

– Older adults. Thyroid issues tend to progress with age. Low TSH may affect the elderly more adversely.

– Individuals with sleep disorders or sleep deprivation. Poor sleep exacerbates the effects of low TSH.

– Those with cardiovascular problems. The increased heart demands worsen problems like hypertension or heart failure.

– People taking medications that lower TSH long-term, like high dose steroids.

– Anyone with major nutrient deficiencies that reduce energy, like iron deficiency.

However, even in milder cases of low TSH, fatigue is still a possible symptom. Anyone with a TSH below the reference range could experience some degree of exhaustion. Monitoring for other hyperthyroid symptoms is important.

How is low TSH diagnosed?

If symptoms lead a doctor to suspect hyperthyroidism or thyroid dysregulation, they will typically order a thyroid panel of blood tests. This normally includes:

– TSH level – Low TSH indicates underactivity of the pituitary gland or hyperthyroidism.

– Free T4 level – Measures the unbound and active form of thyroxine. High levels confirm hyperthyroidism.

– Free T3 level – Like T4, elevated T3 indicates excess thyroid hormones.

Based on results and clinical evaluation, additional testing may help determine the cause of low TSH:

– Thyroid antibodies – High levels can indicate autoimmune thyroiditis or Graves’ disease.

– Thyroid ultrasound – Checks thyroid gland size and appearance.

– Radioactive iodine uptake – Measures how much iodine the thyroid takes up. High uptake points to hyperthyroidism.

– Pituitary MRI – If TSH is low but T4/T3 normal, a pituitary adenoma may be suppressing TSH production.

Diagnosing the reason for low TSH guides appropriate treatment.

Treatments for fatigue from low TSH

Treatment focuses on resolving the underlying condition causing low TSH. This helps normalize thyroid hormone levels and alleviate associated fatigue.

For hyperthyroidism, common treatments include:

– Antithyroid medications – Methimazole, carbimazole, propylthiouracil inhibit thyroid hormone production.

– Radioactive iodine – Damages thyroid tissue to reduce hormone secretion. Often leads to hypothyroidism needing thyroid hormone replacement.

– Surgery – Removing part or all of the thyroid gland.

Other tips to reduce fatigue symptoms include:

– Ensure adequate sleep. Use sleep hygiene and avoid sleep disruptors.

– Follow a balanced, nutrient-rich diet. Take supplements like iron if deficient.

– Exercise regularly at a moderate intensity.

– Practice stress management techniques.

– Take prescribed beta-blockers temporarily to control heart symptoms.

– Avoid triggers like caffeine or stimulating medications that exacerbate symptoms.

With treatment of the hyperthyroidism, TSH should return to the normal range and associated fatigue improve.

Outlook for low TSH and fatigue

When caught early, hyperthyroidism leading to low TSH is very treatable. Symptoms like fatigue usually resolve with treatment.

Without treatment, uncontrolled hyperthyroidism can lead to worsening exhaustion, muscle wasting, bone loss, and heart complications. So prompt diagnosis is important.

In cases of non-thyroidal illness lowering TSH, fatigue and TSH levels typically recover when the main disease is treated.

The prognosis is excellent when the underlying disorder is properly addressed. Even transient low TSH causing temporary fatigue is manageable. With the right thyroid treatment, patients can expect normal TSH, thyroid hormones, and energy levels to be restored.


In summary:

– Low TSH is commonly caused by hyperthyroidism, where thyroid hormone levels are too high. It can also result from non-thyroidal illnesses or pituitary disorders.

– Symptoms like fatigue originate from the cascade of metabolic effects of elevated T4 and T3 thyroid hormones.

– Diagnosis is made by testing TSH and thyroid hormone levels, and optionally antibodies and imaging if the cause is unclear.

– Treatment focuses on resolving the underlying disease increasing thyroid hormones. This can normalize TSH and reduce fatigue.

– With proper management, the outlook for low TSH-related fatigue is very good. Symptoms are usually reversible.

So in people with unexplained fatigue, checking TSH and thyroid hormone levels can uncover a possible cause. Addressing the reasons behind low TSH can help alleviate exhaustion when it occurs.