Hypothyroidism

Introduction

Hypothyroidism means the thyroid gland does not make enough thyroid hormone. Metabolism slows, and people commonly notice fatigue, weight gain, cold intolerance, constipation, dry skin, and low mood.

Early symptoms can be subtle and mistaken for aging or stress. Untreated disease can contribute to high cholesterol, heart problems, joint pain, infertility, goiter, and—rarely—life-threatening myxedema coma.

It affects all ages but is much more common in women, especially older women. Babies can be born with congenital hypothyroidism and are screened in many countries with a newborn blood-spot test.

This page covers causes (including Hashimoto’s thyroiditis), symptoms by age, blood tests, levothyroxine treatment, pregnancy considerations, prevention-related habits, complications, and when to seek care. It is general education—not a personal dosing guide.

Overview

The thyroid uses iodine to produce T4 and T3, hormones that set metabolic rate in nearly every tissue. When levels fall, the pituitary usually raises TSH—unless the problem is in the pituitary or hypothalamus (secondary or tertiary hypothyroidism).

Hashimoto’s thyroiditis—an autoimmune attack on the thyroid—is the most common cause in iodine-replete regions. Other causes include radioactive iodine or surgery for hyperthyroidism or thyroid cancer, certain medicines, postpartum thyroiditis, and severe iodine deficiency in endemic areas.

Daily levothyroxine replacement is usually simple, safe, and effective once the dose is individualized with lab monitoring. Most people need lifelong therapy when the gland is permanently underactive.

• Underactive thyroid → low thyroid hormone and slowed metabolism
• Far more common in women than men; can affect infants and children
• Leading cause in many regions: Hashimoto’s autoimmune thyroiditis
• Typical clues: fatigue, weight gain, cold sensitivity, constipation, dry skin
• Key test: TSH (often high); free T4 low or low-normal; antibodies when indicated
• Standard treatment: daily levothyroxine with periodic blood monitoring
• Pregnancy and myxedema require specialist urgency

What happens in the body

In primary hypothyroidism the thyroid itself fails. Autoimmune inflammation (Hashimoto’s) destroys hormone-producing cells and often raises anti-TPO antibodies; a goiter may be present. After radioiodine or thyroidectomy, too little functional tissue remains.

Lymphocytic thyroiditis after pregnancy may swing from a hyperthyroid phase to months of hypothyroidism; some women recover and some stay underactive. Pituitary injury lowers TSH (secondary), and hypothalamic disease lowers TRH drive (tertiary), so TSH may be low or inappropriately normal despite low thyroid hormones.

Medicines such as methimazole, propylthiouracil, lithium, and iodine-rich drugs like amiodarone can impair thyroid hormone availability. Severe dietary iodine deficiency still causes hypothyroidism in parts of the world, including some mountain regions.

• Low T4/T3 slows cellular metabolism throughout the body
• High TSH marks primary thyroid failure; low TSH suggests pituitary/hypothalamic cause
• Anti-TPO antibodies support Hashimoto’s thyroiditis
• Postpartum lymphocytic thyroiditis can be transient or permanent
• Iodine deficiency and selected drugs disrupt hormone synthesis or release
• Chronic stimulation of a failing gland can enlarge it into a goiter

Signs and symptoms

Symptoms vary with severity and age. Common features include:

• Fatigue and low energy
• Increased sensitivity to cold
• Constipation
• Dry skin and thinning hair
• Weight gain
• Puffy face and hoarse voice
• Muscle weakness, aches, stiffness; joint pain or swelling
• Heavier or irregular menstrual periods
• Slowed heart rate
• Depression and impaired memory or slowed thinking
• Elevated blood cholesterol
• Goiter (enlarged thyroid) with progressive disease
• Infants: jaundice, large tongue, puffy face, feeding difficulty, poor growth, low tone, excess sleepiness
• Children/teens: poor growth/short stature, delayed teeth, delayed puberty, learning concerns
• Advanced myxedema: low temperature, low breathing, low blood pressure, unresponsiveness, coma

Causes and risk factors

Clinicians look for primary thyroid failure first, then central causes and drugs. Important contributors include:

• Hashimoto’s thyroiditis (autoimmune; often familial)
• Thyroid destruction after radioactive iodine or surgery
• Lymphocytic (including postpartum) thyroiditis
• Medications: antithyroid drugs, lithium, amiodarone, iodine solutions
• Pituitary disease causing secondary hypothyroidism
• Hypothalamic disease causing tertiary hypothyroidism
• Severe iodine deficiency
• Neck or upper-chest radiation
• Women older than 60; other autoimmune diseases (e.g., rheumatoid arthritis, lupus)
• Family history of thyroid disease
• Recent pregnancy (within about six months) as a risk window

Diagnosis and evaluation

Blood tests confirm the diagnosis and help locate the cause:

• Clinical suspicion from fatigue, cold intolerance, constipation, dry skin, and related signs
• Serum TSH as the primary screening test for primary hypothyroidism
• Free T4 (and sometimes T3) to confirm hormone deficiency
• Thyroid antibody testing (e.g., anti-TPO) when autoimmune disease is likely
• Recognition that early disease may show high TSH with still-normal T4
• Low or inappropriately normal TSH with low T4 raises concern for pituitary/hypothalamic disease
• TRH testing or full pituitary work-up and brain MRI when central hypothyroidism is suspected
• Thyroid imaging or scan selectively when structural disease needs clarification
• Newborn screening blood-spot testing for congenital hypothyroidism

Treatment and management

Levothyroxine replaces missing hormone. Dose changes and combination therapies should only follow clinician advice:

• Daily levothyroxine tablets, usually lifelong when the gland is permanently underactive
• Start low and titrate using follow-up TSH (and free T4) until stable—often yearly checks once controlled
• Take on an empty stomach with water; wait about 30 minutes before food; separate interacting supplements/drugs as advised
• If a dose is missed, take it when remembered unless your clinician gave different instructions
• Mild subclinical cases may be observed with repeat labs if symptoms are absent—individual decision
• Avoid routine T4+T3 combination therapy unless a specialist recommends it; evidence for routine use is limited
• Do not suppress TSH aggressively except in selected thyroid-cancer protocols—risks include atrial fibrillation and bone loss
• Pregnancy: optimize treatment before conception and monitor closely with endocrine guidance
• Supportive habits: not smoking, regular activity, stress reduction, moderate iodine intake, limiting excess dietary fat

Prevention, self-care, and lifestyle

Not every condition is fully preventable, but the steps below may lower risk or recurrence:

• Autoimmune hypothyroidism itself is not reliably preventable
• Adequate—not excessive—dietary iodine supports thyroid hormone production
• Know personal risk after radioiodine, thyroid surgery, or neck radiation and keep lab follow-up
• Watch for symptoms after pregnancy and seek testing if fatigue, cold intolerance, or mood change persist
• Screening high-risk or symptomatic people finds subclinical disease earlier
• Avoid smoking and maintain physical activity and healthy weight as general endocrine supports
• Use clinician guidance on fluoride/iodine extremes and interacting medicines

Possible complications

Delay, missed care, or unsafe self-medication can raise the chance of complications in some cases:

• Goiter and progressive metabolic slowing
• Dyslipidemia and increased cardiovascular risk
• Infertility and menstrual disturbance
• Depression, cognitive slowing, and reduced quality of life
• Myxedema coma—rare but life-threatening
• Growth and developmental impairment in untreated infants and children
• Pregnancy complications if undertreated
• Overtreatment risks: palpitations, anxiety, bone loss, atrial fibrillation

When to see a doctor or seek emergency care

Seek prompt medical advice or emergency care if any of the following apply—it is safer not to wait and see:

• Persistent fatigue, weight gain, cold intolerance, constipation, or low mood
• Neck swelling suggestive of goiter
• Planning pregnancy or newly pregnant with known thyroid disease
• Newborn or infant feeding problems, jaundice, poor growth, or extreme sleepiness
• Child with poor growth or delayed puberty
• Confusion, extreme low body temperature, slow breathing, or unresponsiveness—emergency care (possible myxedema)
• Heart symptoms after starting or changing thyroid hormone dose

Living with the condition

Most people feel well on a stable levothyroxine dose. Keep taking tablets consistently, attend lab checks, and tell clinicians about new medicines, soy/fiber supplements, or pregnancy plans that can change requirements.

Symptom improvement may take weeks after a dose change. Track energy, weight, mood, and cold tolerance, and bring notes to visits rather than adjusting tablets on your own.

Partner with your clinician on cardiovascular risk factors and bone health if you have long-standing disease or need TSH suppression for cancer follow-up.

Frequently asked questions

What causes hypothyroidism?

Hashimoto’s thyroiditis is the most common cause in many countries. Other causes include thyroid surgery or radioiodine, medicines, pituitary/hypothalamic disease, postpartum thyroiditis, and severe iodine deficiency.

How is it diagnosed?

A TSH blood test is the main screen for primary disease, usually with free T4. Antibodies and imaging or pituitary evaluation are added when the cause is unclear.

How is hypothyroidism treated?

Daily levothyroxine replaces missing hormone. Dose is adjusted with blood tests; most people with permanent hypothyroidism take it lifelong.

Can it be prevented?

Autoimmune disease cannot reliably be prevented, but iodine sufficiency, risk-based screening, and prompt treatment of early symptoms prevent many complications.

Is hypothyroidism more common in women?

Yes. Women are affected far more often than men, and risk rises with age and after pregnancy in some forms of thyroiditis.

What are risks in pregnancy?

Undertreated hypothyroidism can harm mother and baby. Women with known disease need preconception optimization and close lab monitoring during pregnancy.

Do I need T3 as well as T4?

Most people do well on levothyroxine alone. Combination T4/T3 therapy is not routine and should only be considered with a specialist when clearly indicated.

When is hypothyroidism an emergency?

Myxedema with hypothermia, slow breathing, low blood pressure, or coma is a medical emergency—call emergency services immediately.

Important caution

This information is for general education only and is not a substitute for personalised medical advice, diagnosis, or treatment.

See a clinician for suspected underactive thyroid, and seek emergency care for signs of myxedema or severe metabolic decompensation.