Also known as: Hypothyroidism (Underactive Thyroid)
Hypothyroidism occurs when the thyroid doesn't produce enough thyroid hormones.
Hypothyroidism is a common endocrine disorder in which the thyroid gland, a butterfly-shaped organ located in the front of the neck, does not produce sufficient amounts of thyroid hormones (thyroxine or T4, and triiodothyronine or T3). These hormones play a critical role in regulating virtually every metabolic process in the body, including energy production, body temperature, heart rate, brain function, and growth. When thyroid hormone levels are insufficient, metabolic processes slow down, affecting nearly every organ system and causing a wide range of symptoms.
The most common cause of hypothyroidism in developed countries is Hashimoto's thyroiditis, an autoimmune condition in which the immune system gradually destroys the thyroid gland. Other causes include previous thyroid surgery, radioactive iodine treatment for hyperthyroidism, radiation therapy to the head or neck, certain medications (lithium, amiodarone, interferon), and iodine deficiency (still the leading cause globally). Less commonly, pituitary gland dysfunction (secondary hypothyroidism) or hypothalamic disease (tertiary hypothyroidism) can reduce thyroid-stimulating hormone (TSH) production, leading to decreased thyroid output.
Hypothyroidism affects approximately 5 percent of the adult population, with women being five to eight times more likely to be affected than men. The condition typically develops slowly over months to years, and early symptoms may be subtle and attributed to aging, stress, or depression. Left untreated, hypothyroidism can lead to serious complications including cardiovascular disease, infertility, peripheral neuropathy, and in extreme cases, myxedema coma. Fortunately, hypothyroidism is readily diagnosed with a simple blood test and effectively treated with daily thyroid hormone replacement therapy.
People with Hypothyroidism often experience the following symptoms.
Profound, persistent fatigue is the most common complaint in hypothyroidism. Reduced thyroid hormone levels slow cellular energy production throughout the body, leaving patients feeling exhausted, sluggish, and unable to sustain normal activity levels despite adequate sleep.
Thyroid hormones help regulate body temperature through their effect on metabolic rate. With insufficient thyroid hormone, the body generates less heat, causing patients to feel cold when others are comfortable. Cold hands and feet are particularly common.
A slowed metabolic rate leads to weight gain, typically 5-15 pounds, even without increased food intake. Much of the initial weight gain is from fluid retention and accumulation of mucopolysaccharides in tissues rather than fat. Significant obesity is not typical of hypothyroidism alone.
Reduced metabolic activity decreases sweat and oil gland function, causing the skin to become dry, rough, and flaky. Nails become brittle and grow slowly. In severe cases, the skin may develop a yellowish tinge from impaired conversion of carotene to vitamin A.
Thyroid hormones are essential for the hair growth cycle. Hypothyroidism causes diffuse hair thinning, particularly noticeable at the outer third of the eyebrows (known as the Queen Anne sign). Hair becomes coarse, dry, and fragile, and may fall out in clumps.
Slowed gastrointestinal motility from reduced metabolic activity leads to infrequent bowel movements, hard stools, and straining. Constipation is one of the more consistent gastrointestinal symptoms and may be the presenting complaint in some patients.
Thyroid hormones are essential for normal brain function. Hypothyroidism can cause depressed mood, difficulty concentrating, memory problems (brain fog), and slowed thinking. These symptoms are frequently misdiagnosed as primary depression, particularly in older adults.
Reduced thyroid hormone impairs muscle metabolism, causing weakness, aching, stiffness, and cramps. Elevated creatine kinase levels may be found on blood tests. Carpal tunnel syndrome is also more common in hypothyroid patients due to tissue swelling.
Certain factors may increase your likelihood of developing Hypothyroidism.
Common approaches to managing hypothyroidism. Always consult a healthcare provider for personalized treatment.
Levothyroxine is the standard treatment for hypothyroidism, providing a synthetic form of the T4 hormone that the body converts to active T3 as needed. Taken once daily on an empty stomach (30-60 minutes before breakfast), it effectively restores normal thyroid hormone levels in most patients. Dosing is individualized based on body weight, age, and TSH levels.
Starting doses are typically 25-50 mcg daily for most adults, with gradual increases every 6-8 weeks based on TSH levels until the target range (usually 0.5-2.5 mIU/L) is achieved. Once stable, TSH is monitored every 6-12 months. Dose adjustments may be needed with weight changes, pregnancy, aging, or medication interactions.
Some patients who do not feel well on levothyroxine alone may benefit from the addition of liothyronine (synthetic T3). While routine combination therapy is not recommended by most guidelines due to inconsistent evidence, it is used in selected cases under specialist supervision when persistent symptoms occur despite optimized T4 therapy.
Many substances interfere with levothyroxine absorption, including calcium supplements, iron supplements, antacids, proton pump inhibitors, cholestyramine, and soy products. These should be taken at least 4 hours apart from levothyroxine. Patients should maintain consistent timing and conditions for taking their medication.
When Hashimoto's thyroiditis is the underlying cause, treatment focuses on thyroid hormone replacement, as there is currently no therapy to halt the autoimmune destruction. Selenium supplementation may modestly reduce thyroid antibody levels. Regular monitoring is important as hormone requirements may increase over time as more thyroid tissue is destroyed.
Hypothyroidism is diagnosed primarily through blood tests measuring thyroid-stimulating hormone (TSH) and free thyroxine (free T4). An elevated TSH with a low free T4 confirms primary hypothyroidism, while a high TSH with a normal free T4 indicates subclinical hypothyroidism, an early stage where the pituitary gland is working harder to stimulate the thyroid. Thyroid peroxidase antibodies (TPO antibodies) are measured to identify Hashimoto's thyroiditis as the underlying cause, present in approximately 90 percent of cases. Additional tests may include free T3, thyroglobulin antibodies, and thyroid ultrasound to evaluate gland structure and detect nodules. Lipid panels often show elevated cholesterol in hypothyroid patients. Screening is recommended for women over 35 every 5 years, during pregnancy, and for patients with risk factors including family history of thyroid disease, other autoimmune conditions, previous neck radiation, or symptoms suggestive of thyroid dysfunction.
Steps that may help reduce the risk of developing or worsening hypothyroidism.
Ensure adequate iodine intake through iodized salt, seafood, dairy products, and eggs, as iodine is an essential building block for thyroid hormone production, though excessive iodine should also be avoided.
Be aware of family history of thyroid disease and request screening if you have a first-degree relative with hypothyroidism or Hashimoto's thyroiditis, as early detection allows prompt treatment.
Inform your doctor if you are taking medications known to affect thyroid function, including lithium, amiodarone, interferon-alpha, or immune checkpoint inhibitors, so that thyroid function can be monitored.
Manage stress and prioritize adequate sleep, as chronic stress may influence immune function and potentially exacerbate autoimmune thyroid conditions in genetically susceptible individuals.
Request thyroid screening during pregnancy planning and early pregnancy, as undiagnosed hypothyroidism can adversely affect fertility and fetal development, and thyroid hormone requirements increase during pregnancy.
If left untreated or poorly managed, hypothyroidism may lead to:
In most cases, yes. Hypothyroidism caused by Hashimoto's thyroiditis or thyroid surgery is permanent and requires lifelong levothyroxine therapy. However, some forms of hypothyroidism may be temporary, including postpartum thyroiditis (which resolves in most women within 12-18 months), subacute thyroiditis, and drug-induced hypothyroidism that may reverse when the offending medication is stopped. Your doctor can advise whether a trial of medication withdrawal is appropriate.
Hypothyroidism typically causes modest weight gain of 5-15 pounds, mostly from fluid retention and slowed metabolism rather than fat accumulation. Once thyroid levels are normalized with levothyroxine, you can expect to lose the weight related to fluid retention. However, significant weight loss beyond this is unlikely from thyroid treatment alone, and maintaining a healthy weight requires balanced diet and regular exercise regardless of thyroid status.
Take levothyroxine on an empty stomach, ideally 30-60 minutes before breakfast or at bedtime at least 3 hours after your last meal. Swallow with water only, not coffee, juice, or milk. Avoid taking calcium, iron, or antacid supplements within 4 hours. Take it at the same time each day for consistent absorption. If you miss a dose, take it as soon as you remember, or take two doses the next day.
Hypothyroidism is an underactive thyroid producing too little hormone, causing fatigue, weight gain, cold intolerance, and slowed metabolism. Hyperthyroidism is an overactive thyroid producing excess hormone, causing weight loss, rapid heartbeat, heat intolerance, anxiety, and tremors. Both are common thyroid disorders but have opposite effects on the body. Graves' disease is the most common cause of hyperthyroidism, while Hashimoto's thyroiditis is the most common cause of hypothyroidism.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.