In brief
When the thyroid gland does not make enough thyroid hormone. It can cause tiredness, weight gain, feeling cold, constipation and low mood, and it is treatable.
- A high TSH with normal thyroid hormones can mean a mildly underactive thyroid or an acute illness, according to Pathology Tests Explained.
- Untreated hypothyroidism increases the risk of miscarriage and other pregnancy complications.
- Complications of an underactive thyroid include high cholesterol and heart disease.
How it works
healthdirect lists symptoms including unexplained weight gain, a puffy and pale face, brittle hair and nails, thinning hair, dry skin, tiredness, being unable to tolerate the cold, muscle pain, constipation, headache, low mood and irregular or heavier periods.
The most common cause in Australia is Hashimoto's disease. Other causes include thyroid surgery, radiation therapy, some medicines such as lithium, and not getting enough iodine. A blood test diagnoses it, and treatment with thyroid hormone replacement is usually lifelong, with regular checks to adjust the dose.
Connections
12 connections on the map. Select a topic to read its page.
Hypothyroidism (underactive thyroid) can cause
Tiredness is a symptom of an underactive thyroid.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
Being unable to tolerate the cold is a symptom of an underactive thyroid.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
Unexplained weight gain is a symptom of an underactive thyroid.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
Thinning hair is a symptom of an underactive thyroid.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
Low mood, depression or lack of motivation are symptoms of an underactive thyroid.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
- Swelling (fluid retention) Supported
Thyroid problems are one cause of fluid retention, and a puffy face is a symptom of an underactive thyroid.
Sources: healthdirect Australia, Fluid retention; healthdirect Australia, Hypothyroidism (underactive thyroid)
Constipation is a symptom of hypothyroidism.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
Hypothyroidism (underactive thyroid) is linked with
- Fatty liver disease (MAFLD) Supported
An underactive thyroid is a less common cause of fatty liver, according to healthdirect.
Not getting enough iodine is one cause of an underactive thyroid.
Sources: healthdirect Australia, Hypothyroidism (underactive thyroid); NIH Office of Dietary Supplements, Iodine fact sheet for consumers
High cholesterol is a complication of an underactive thyroid.
Source: healthdirect Australia, Hypothyroidism (underactive thyroid)
Hypothyroidism (underactive thyroid) can result from
Hashimoto's disease usually causes hypothyroidism and is its most common cause in Australia.
Sources: healthdirect Australia, Hashimoto's disease; healthdirect Australia, Hypothyroidism (underactive thyroid)
Hypothyroidism (underactive thyroid) is measured by
A high TSH can mean too little thyroid hormone is being produced.
Sources: Pathology Tests Explained, Thyroid stimulating hormone (TSH); Pathology Tests Explained, Thyroid function tests
Lab tests
Medicines and supplements
General education only. Never start, stop or change a medicine without your prescriber.
Sources
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Summarised from healthdirect, Pathology Tests Explained and the Better Health Channel. 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.