Hypothyroidism
Underactive thyroid, including subclinical hypothyroidism
Chronic conditionThe thyroid doesn't make enough hormone, so many body processes slow down. This page covers causes other than Hashimoto's, and mild (subclinical) hypothyroidism.
Medical Disclaimer
For education only — this guide can't diagnose you. If these signs sound familiar, talk with a healthcare provider. Book a consult
What happens
Thyroid hormone sets the pace of your metabolism, heart rate, and energy. Hashimoto's, the most common cause in the US, has its own page. Other causes include thyroid surgery, radioactive iodine treatment, too little or too much iodine, and medicines such as lithium, amiodarone, and some cancer immunotherapies. Thyroid inflammation after pregnancy (postpartum thyroiditis) can cause a low phase that usually recovers within a year, though some women stay hypothyroid. Rarely, the pituitary gland doesn't send enough signal (central hypothyroidism), so TSH can look normal while free T4 is low. Subclinical hypothyroidism means TSH is high but free T4 is normal. It often returns to normal on a repeat test, and treating mild cases outside pregnancy hasn't been shown to improve how people feel.
Who gets it
Hypothyroidism is several times more common in women and rises with age. Risk is higher after thyroid surgery, radioactive iodine, or neck radiation, in the year after giving birth, and with lithium or amiodarone. Subclinical hypothyroidism is common in older women, partly because TSH naturally drifts higher with age.
Signs worth getting checked
- Fatigue and sluggishness
- Feeling cold
- Weight gain or difficulty losing weight
- Constipation
- Dry skin, thinning hair, or brittle nails
- Heavier or irregular periods
- Low mood, brain fog, or slowed thinking
- Muscle aches or stiffness
Labs to ask about
- TSH
- Free T4, which is the key test if a pituitary cause is possible
- A repeat TSH and free T4 in 6 to 12 weeks before diagnosing subclinical hypothyroidism
- TPO antibodies to check for Hashimoto's
- Lipid panel and CBC
- Other pituitary hormone tests and an MRI if central hypothyroidism is suspected
Treatments your doctor may discuss
- Thyroid hormone replacement (usually levothyroxine), adjusted with blood tests
- For subclinical hypothyroidism, treatment is usually advised if TSH is above 10, or if you're pregnant or trying to conceive. Milder cases are often monitored.
- Medicines such as lithium or amiodarone are usually continued, with thyroid hormone added if needed
- Combined T4 and T3 therapy may be considered if you still feel unwell on levothyroxine with normal levels. The evidence is mixed.
Supportive steps to discuss with your provider
- Stop biotin supplements 2 days before thyroid blood tests. Biotin can make results look falsely abnormal.
- Ask your provider how to time thyroid medicine. It's usually taken at the same time each day, apart from iron, calcium, and coffee.
- Tell your provider as soon as you're pregnant. Your dose usually needs to go up early in pregnancy.
- Take a prenatal vitamin with iodine during pregnancy and breastfeeding, but avoid high-dose iodine or kelp otherwise.
- Avoid over-the-counter 'thyroid support' products. Some have been found to contain actual thyroid hormone.
See a doctor promptly if you have
- Severe drowsiness, confusion, a very low body temperature, or slow breathing: call 911
- Chest pain or a racing heart after starting or raising thyroid medicine: get same-day care
- You're pregnant or planning pregnancy and have thyroid disease
- Severe headaches or vision changes along with low thyroid levels
- Symptoms that continue despite treatment
Related conditions
Ready to find the root cause?
Dr. Lesher is a Naturopathic Doctor who focuses on autoimmune and chronic conditions in women. Since 2020, she's helped hundreds of patients stop managing symptoms and start healing.