Your thyroid is a small, butterfly-shaped gland at the front of your neck, but it influences almost every part of your body. When it does not make enough thyroid hormone, a condition called hypothyroidism, many body processes slow down. Symptoms creep in gradually and are easy to blame on stress or aging. A simple blood test can find it, and treatment is usually effective.
What does the thyroid do?
The thyroid makes two main hormones, thyroxine (T4) and triiodothyronine (T3). They help control:
- How quickly your body uses energy (metabolism)
- Heart rate
- Body temperature
- Digestion
- Muscle strength
- Brain development in babies and children
- Menstrual cycles and fertility
The pituitary gland in the brain releases thyroid-stimulating hormone (TSH), which tells the thyroid how much hormone to make. When thyroid hormone is low, TSH usually rises as the pituitary tries to push the thyroid to work harder.
Common symptoms
Symptoms develop slowly, often over months or years, and vary from person to person:
- Tiredness and low energy
- Feeling cold when others do not
- Weight gain or difficulty losing weight
- Constipation
- Dry skin and brittle nails
- Thinning hair
- Puffy face
- Hoarse voice
- Muscle aches, stiffness or weakness
- Joint pain
- Slow heart rate
- Heavy or irregular periods
- Low mood or depression
- Slowed thinking or poor memory
- An enlarged thyroid (goiter)
In older adults, symptoms can be subtle or mistaken for normal aging.
What causes hypothyroidism?
Hashimoto’s thyroiditis
In the United States, the most common cause is Hashimoto’s thyroiditis, an autoimmune condition in which the immune system attacks the thyroid. It is much more common in women and often runs in families.
Other causes
- Thyroid surgery that removes part or all of the gland
- Radioactive iodine treatment for an overactive thyroid
- Radiation therapy to the head or neck
- Certain medicines, including lithium and amiodarone
- Inflammation of the thyroid (thyroiditis), including after pregnancy
- Problems with the pituitary gland (uncommon)
- Too little iodine in the diet, which is the leading cause worldwide but less common where salt is iodized
- Congenital hypothyroidism, which is present at birth and checked through newborn screening
Who is at higher risk
- Women, especially over age 60
- People with a family history of thyroid disease
- People with other autoimmune conditions such as type 1 diabetes, celiac disease or rheumatoid arthritis
- People who have been pregnant or given birth in the past six months
- People who have had thyroid treatment or neck radiation
How hypothyroidism is diagnosed
Diagnosis is based on symptoms and blood tests:
Keep reading
The rest of this guide is free. Watch a short ad to unlock it and support independent health writing.
Preparing your ad…
- TSH: usually the first test. A high TSH suggests an underactive thyroid. Many laboratories use a reference range of roughly 0.4 to 4.0 mIU/L, though ranges vary by lab, age and pregnancy.
- Free T4: shows how much active hormone is circulating.
- Thyroid antibodies (such as TPO antibodies): help confirm Hashimoto’s.
| Result pattern | What it usually means |
|---|---|
| High TSH, low free T4 | Overt hypothyroidism |
| High TSH, normal free T4 | Subclinical (mild) hypothyroidism |
| Normal TSH, normal free T4 | Normal thyroid function |
In subclinical hypothyroidism, TSH is raised but T4 is normal. Some people need treatment and others are simply monitored, depending on TSH level, symptoms, age, pregnancy plans and antibody status.
Treatment
The standard treatment is levothyroxine, a synthetic form of T4 taken by mouth once a day.
- The dose is based on your weight, age, heart health and TSH level.
- Your TSH is usually rechecked about 6 to 8 weeks after starting or changing the dose.
- Once the dose is stable, TSH is generally checked once a year or as advised.
- Most people need treatment for life.
Tips for taking levothyroxine
- Take it at the same time each day, ideally on an empty stomach with water, 30 to 60 minutes before breakfast, or at bedtime as directed.
- Separate it by several hours from calcium, iron, antacids and some other supplements, which can block absorption.
- Tell your clinician before switching brands or formulations.
- Do not stop or change your dose without advice.
Too much thyroid hormone can cause symptoms of an overactive thyroid, such as a racing heart, anxiety, poor sleep and bone loss over time, which is why regular monitoring matters.
Hypothyroidism and pregnancy
Thyroid hormone is vital for a baby’s brain development. Women with hypothyroidism who are planning pregnancy or become pregnant usually need their dose increased and checked more often. Contact your clinician as soon as you know you are pregnant.
Living well with hypothyroidism
- Keep up with blood tests and appointments.
- Eat a balanced diet. Most people do not need special thyroid diets or iodine supplements; too much iodine can also cause thyroid problems.
- Stay active; exercise helps energy and weight.
- Ask about other causes if tiredness continues despite normal TSH levels, such as anemia, vitamin deficiencies, sleep problems or depression.
The NIDDK hypothyroidism guide has more detail.
Frequently asked questions
Can hypothyroidism cause weight gain?
It can cause modest weight gain, mostly from fluid and a slower metabolism. Treatment often helps, but it is not usually a major weight-loss solution on its own.
Are natural thyroid supplements a good idea?
Over-the-counter “thyroid support” supplements are not regulated like medicines, may contain variable amounts of hormone or iodine, and can interfere with test results. Talk with your clinician first.
Can hypothyroidism go away?
Some types, such as thyroiditis after pregnancy, can be temporary. Hashimoto’s and hypothyroidism after surgery or radioactive iodine are usually permanent.
The bottom line
Hypothyroidism is common, especially in women, and its symptoms are easy to overlook. If you have ongoing tiredness, feel cold, gain weight or notice other symptoms on this list, ask your clinician about a TSH test. With the right daily dose of levothyroxine and regular checks, most people feel well.
This article is for general information and is not a substitute for advice from a qualified healthcare professional.