Hormones made by the thyroid gland, mainly thyroxine (T4) and tri-iodothyronine (T3). They regulate metabolism, including growth and energy use.

Thyroid stimulating hormone (TSH) from the pituitary gland prompts the thyroid to release more T4 and T3.
People with Hashimoto's disease may need to take levothyroxine for life.
Biotin supplements should not be taken for two days before a thyroid blood test.

How it works

The thyroid makes mostly T4. T3 is more active but is made in smaller amounts. The more T3 and T4 in the blood, the faster the metabolism, and thyroid hormones also influence energy levels, body temperature and calcium levels.

Too little thyroid hormone causes an underactive thyroid (hypothyroidism), which is treated with thyroid hormone replacement. Too much causes an overactive thyroid (hyperthyroidism). Blood tests check TSH first, then free T4 and free T3 if needed.

Connections

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Thyroid hormones (T4 and T3) is made by

Thyroid gland
The thyroid makes thyroxine (T4) and tri-iodothyronine (T3). T3 is more active but is made in smaller amounts.
Source: Better Health Channel (Victorian Government), Thyroid gland

Thyroid hormones (T4 and T3) is linked with

Mitochondria (cell energy)
Thyroid hormones regulate metabolism, including energy use, and mitochondria generate most of the energy cells use.
Sources: Better Health Channel (Victorian Government), Thyroid gland; National Human Genome Research Institute (NIH), Mitochondria, Talking Glossary of Genomic and Genetic Terms

Lab tests

Thyroid function tests (TSH, free T4, free T3)Blood tests that show how well your thyroid is working. TSH is usually measured first, and free T4 and free T3 are added if TSH is abnormal.

Medicines and supplements

General education only. Never start, stop or change a medicine without your prescriber.

Thyroid hormone (levothyroxine)Hormones

Sources

Thyroid glandBetter Health Channel (Victorian Government), last reviewed 6 December 2015
Endocrine glands and their hormoneshealthdirect Australia, last reviewed December 2024
Thyroid function testsPathology Tests Explained, last reviewed 9 January 2025
Hypothyroidism (underactive thyroid)healthdirect Australia, last reviewed October 2024
Hashimoto's diseasehealthdirect Australia, last reviewed September 2024

Each connection above names its own source. See every source AskBioMap uses.

Summarised from the Better Health Channel, healthdirect and Pathology Tests Explained. Sources read on 13, 16 and 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.

In brief