Hypothyroidism Symptoms: Is Your Thyroid Underactive?

Hypothyroidism (underactive thyroid) affects approximately 5% of the population and is significantly more common in women, particularly after age 60. Hashimoto's thyroiditis — an autoimmune condition — is the most common cause in iodine-sufficient countries. Thyroid hormone regulates metabolism in virtually every cell of the body, so deficiency produces a wide range of symptoms.

Classic symptoms develop gradually and are often attributed to normal aging or stress: persistent fatigue and sluggishness, weight gain despite no change in diet, feeling cold when others are comfortable, constipation, dry skin and hair, hair loss (including the outer third of eyebrows), puffy face and eyes, slow heart rate, muscle weakness and aches, depression and cognitive slowing, and heavy or irregular menstrual periods.

Diagnosis is straightforward with a TSH (thyroid stimulating hormone) blood test. Elevated TSH indicates the pituitary is working harder to stimulate an underperforming thyroid. Free T4 levels confirm the diagnosis. Anti-TPO antibodies identify autoimmune Hashimoto's as the cause.

Treatment is highly effective: synthetic levothyroxine (T4) taken once daily restores normal thyroid hormone levels in most patients. Doses are adjusted based on TSH levels every 6–8 weeks until optimized. Most patients notice significant improvement in energy, mood, and weight within 2–4 weeks of starting treatment. Medication is typically lifelong.

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