What are the symptoms of hypothyroidism (underactive thyroid)?

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From the Guidelines

Hypothyroidism symptoms include fatigue, feeling cold, weight gain, hair loss, and constipation, which can develop slowly over years and may be subtle at first. These symptoms occur because the thyroid gland doesn't produce enough thyroid hormones, which regulate metabolism throughout the body 1. When thyroid hormone levels are low, bodily functions slow down, causing these symptoms.

Key Symptoms

  • Fatigue
  • Feeling cold
  • Weight gain
  • Hair loss
  • Constipation According to the U.S. Preventive Services Task Force recommendation statement 1, subclinical hypothyroidism is defined as an asymptomatic condition in which a patient has a serum thyroid-stimulating hormone (TSH) level exceeding the upper threshold of a specified laboratory reference interval, but a normal thyroxine (T4) level. However, overt hypothyroidism does not require the presence of symptoms and has been defined biochemically by an elevated TSH level and a low T4 level, which may or may not be associated with a set of relatively subtle and nonspecific clinical symptoms 1. Severe, untreated hypothyroidism can lead to myxedema, a rare but potentially life-threatening condition requiring immediate medical attention. If you experience these symptoms, especially if they're new, persistent, or worsening, consult a healthcare provider for proper diagnosis through blood tests measuring thyroid hormone levels.

From the Research

Symptoms of Hypothyroidism

The symptoms of hypothyroidism can vary and may not be specific, making it challenging to diagnose in some cases 2, 3, 4, 5. Some common symptoms include:

  • Fatigue
  • Weight gain
  • Increased sensitivity to cold (cold intolerance)
  • Irregular bowel movements (constipation)
  • Dry skin (xeroderma)
  • Voice changes
  • Lethargy

Causes of Symptoms

These symptoms are mostly the result of a low metabolic rate in the body, which can be caused by a variety of factors, including:

  • Autoimmune diseases
  • Radiation therapy
  • Thyroid gland removal surgeries
  • Certain medications
  • Chronic autoimmune thyroiditis (Hashimoto's thyroiditis)
  • Iodine deficiency

Diagnosis and Treatment

The diagnosis of hypothyroidism is based on laboratory tests that measure the levels of thyroid hormones (T3 and T4) in the blood 2, 3, 4, 5. Treatment typically involves lifelong hormone replacement therapy with synthetic thyroid hormone replacement medication, such as levothyroxine, to help regulate hormone levels in the body 2, 3, 4, 5.

Management of Symptoms

Lifestyle modifications like eating healthy food and exercising regularly can help manage the symptoms and improve the quality of life 2. However, some patients may experience persistent symptoms despite adequate levothyroxine dosing, and may need to be reassessed for other causes or the need for referral 3.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Hypothyroidism: Diagnosis and Treatment.

American family physician, 2021

Research

Hypothyroidism.

Lancet (London, England), 2017

Research

Hypothyroidism.

Lancet (London, England), 2024

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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