What is hypothyroidism?
Hypothyroidism, or an underactive thyroid, means the butterfly-shaped gland in your neck isn't making enough thyroid hormone (T4 and T3), so your metabolism slows. In places with enough dietary iodine, the most common cause is Hashimoto's thyroiditis, where the immune system attacks the thyroid. It can also follow thyroid surgery or radioactive iodine (Chaker et al., 2017). It's more common in women and older adults.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
What are the symptoms?
| Area | Common symptoms |
|---|---|
| General | Fatigue, sluggishness, feeling cold |
| Weight and digestion | Weight gain, constipation |
| Skin and hair | Dry skin, hair loss |
| Mood and thinking | Low mood, brain fog |
| Other | Puffy face, irregular periods, higher cholesterol |
Because symptoms come on slowly and are so common, they're easy to write off as being tired. Low thyroid hormone can also push up LDL cholesterol.
How is it diagnosed and treated?
A blood test showing high TSH (thyroid-stimulating hormone) and low free T4 confirms hypothyroidism. If TSH is only mildly high and T4 is normal, it's called subclinical hypothyroidism, which is sometimes just monitored depending on the numbers, age and symptoms. Standard treatment is a daily dose of levothyroxine, a synthetic T4 (Jonklaas et al., 2014). It's usually taken on an empty stomach in the morning, separated from iron or calcium supplements, and the dose is adjusted by rechecking TSH every 6–8 weeks.
FAQ
- Does hypothyroidism make you gain a lot of weight?
- It can cause some weight gain, but usually a modest amount, much of it fluid. Some of it comes off with treatment.
- Will I need medication for life?
- With Hashimoto's or after thyroid surgery, usually yes. Some forms, like temporary thyroiditis, resolve, so talk it through with your doctor.
Sources reviewed: 2026-10-25
See also: Thyroid Nodules
References
- Chaker, L., Bianco, A. C., Jonklaas, J., & Peeters, R. P. (2017). Hypothyroidism. The Lancet, 390(10101), 1550–1562.
- Jonklaas, J., Bianco, A. C., Bauer, A. J., et al. (2014). Guidelines for the treatment of hypothyroidism. Thyroid, 24(12), 1670–1751.