What Is Hypothyroidism?
Hypothyroidism is a condition in which the thyroid gland — a butterfly-shaped gland at the base of the neck — does not produce enough thyroid hormone to meet the body's needs. Since thyroid hormones (primarily T3 and T4) regulate metabolism, energy production, body temperature, heart rate, and many other essential functions, a deficiency can affect virtually every system in the body.
Hypothyroidism is one of the most common endocrine disorders worldwide. It affects women more often than men and becomes increasingly prevalent with age. In many cases, it develops gradually, with symptoms so subtle that they're dismissed as normal aging or stress — making early recognition important.
Causes of Hypothyroidism
Hashimoto's Thyroiditis (Most Common)
An autoimmune condition in which the immune system mistakenly attacks the thyroid gland, progressively damaging its ability to produce hormones. It often runs in families and may be associated with other autoimmune conditions like type 1 diabetes or rheumatoid arthritis.
Other Common Causes
- Previous thyroid surgery — partial or full removal of the thyroid
- Radioactive iodine treatment for hyperthyroidism or thyroid cancer
- Iodine deficiency — less common in developed countries with iodized salt
- Certain medications — including lithium and amiodarone
- Congenital hypothyroidism — present from birth
- Pituitary dysfunction — secondary hypothyroidism due to inadequate TSH production
Symptoms: What Hypothyroidism Feels Like
Because thyroid hormones influence so many body systems, the symptom profile is broad. Key symptoms include:
- Fatigue and sluggishness — often the most prominent complaint
- Weight gain despite no changes in diet or activity
- Feeling cold — especially in the hands and feet
- Dry skin, hair, and brittle nails
- Hair loss, including thinning of the outer eyebrows
- Constipation
- Brain fog — poor concentration and memory difficulties
- Low mood and depression
- Slow heart rate (bradycardia)
- Muscle weakness or aches
- Elevated cholesterol levels
- Menstrual irregularities in women
Diagnosis: What Tests Are Used?
Hypothyroidism is diagnosed primarily through blood tests:
| Test | What It Measures | In Hypothyroidism |
|---|---|---|
| TSH (Thyroid-Stimulating Hormone) | Pituitary signal to the thyroid | Elevated (thyroid not responding adequately) |
| Free T4 | Inactive thyroid hormone in blood | Low or low-normal |
| Free T3 | Active thyroid hormone in blood | May be low in conversion issues |
| TPO Antibodies | Autoimmune markers | Elevated in Hashimoto's |
TSH is typically the first-line test. A persistently elevated TSH, particularly when paired with low Free T4 and symptoms, confirms hypothyroidism. Subclinical hypothyroidism — elevated TSH with normal T4 and mild or no symptoms — is monitored and sometimes treated depending on severity and individual circumstances.
Treatment: Thyroid Hormone Replacement
Levothyroxine (Synthroid, Euthyrox)
The standard treatment is synthetic T4 (levothyroxine), taken once daily, usually in the morning on an empty stomach. The body converts T4 to the active T3 form as needed. Most people respond well to levothyroxine, with symptoms improving over several weeks to months as the dose is optimized.
T3/T4 Combination Therapy
A minority of patients continue to have symptoms on levothyroxine alone. In some cases, adding synthetic T3 (liothyronine) or switching to desiccated thyroid extract (which contains both T3 and T4) may be explored in consultation with an endocrinologist.
Ongoing Monitoring
Once on treatment, TSH should be rechecked every 6–12 months, or sooner if symptoms change. Dose adjustments may be needed over time, particularly during pregnancy, significant weight changes, or after starting new medications.
Living Well With Hypothyroidism
With the right diagnosis and appropriate treatment, most people with hypothyroidism lead full, healthy lives. Consistent medication adherence, regular monitoring, and a healthy lifestyle — including adequate sleep, stress management, and a nutrient-rich diet — all play a role in maintaining optimal thyroid health over the long term.