The thyroid gland is a small butterfly-shaped gland in the neck. When it is underactive or overactive, it produces a wide range of symptoms throughout the body.
Written & Reviewed by
MBBS (Col) · MD (Col) · SLMC No. 27329 · Medical Director, Sineth Hospitals
🩺 Medically Reviewed📅 June 2026
The thyroid gland is a small, butterfly-shaped gland located at the front of the neck. It produces hormones that control metabolism, energy use, body temperature, heart rate, and many other vital functions throughout the body.
When the thyroid becomes underactive or overactive, a wide range of symptoms can develop — many of which are vague and easily confused with other conditions. This guide explains the most common thyroid symptoms and the tests used to diagnose thyroid disease.
Overview
What is the thyroid gland?
The thyroid gland sits in the lower front of the neck, just below the Adam's apple. It is part of the endocrine system and plays a central role in regulating how the body uses energy.
The thyroid hormone pathway works like this:
Pituitary gland releases TSH (thyroid-stimulating hormone)
TSH signals the thyroid gland to produce hormones
Thyroid produces T4 (thyroxine) and T3 (triiodothyronine)
T3 and T4 act on almost every tissue and organ in the body
Why does this matter?Because thyroid hormones affect so many body systems, a problem with the thyroid can produce symptoms across multiple parts of the body — from the heart to the skin to mental health — making it easy to miss without proper testing.
Types
Two main types of thyroid disease
Most thyroid symptoms fall into one of two categories, depending on whether the thyroid is producing too little or too much hormone.
| Type | What it means | Common causes |
|---|---|---|
| Hypothyroidism (underactive thyroid) | The thyroid does not produce enough hormones. Body processes slow down. | Hashimoto's thyroiditis, iodine deficiency, post-thyroid surgery, certain medicines |
| Hyperthyroidism (overactive thyroid) | The thyroid produces too much hormone. Body processes speed up. | Graves' disease, toxic nodular goitre, thyroiditis |
Important: Thyroid disease is very common, especially in women. Many people have thyroid problems for years without realising it because the symptoms develop gradually and can be attributed to stress, ageing, or lifestyle.
Hypothyroidism
10 symptoms of hypothyroidism (underactive thyroid)
When thyroid hormone levels are too low, metabolism slows down. Symptoms tend to develop gradually and are often subtle at first.
1. Fatigue and persistent tiredness
Persistent tiredness that is not relieved by sleep is one of the most common symptoms of hypothyroidism. Reduced thyroid hormone levels slow down metabolism and reduce energy production throughout the body.
2. Weight gain
An underactive thyroid slows metabolism, causing the body to burn fewer calories. This leads to gradual weight gain that is difficult to control even with a normal diet and activity level.
3. Cold intolerance
People with hypothyroidism often feel cold even in warm environments. This happens because reduced thyroid hormone levels lower the body's ability to generate and regulate heat.
4. Dry skin
Slow metabolism reduces sweat gland activity and cell turnover, leading to dry, rough, or flaky skin. The skin may also appear pale and feel cool to the touch.
5. Hair loss and hair thinning
Thyroid hormones are needed for healthy hair growth. In hypothyroidism, hair may become dry, brittle, coarse, or fall out in larger amounts than usual, including from the outer edges of the eyebrows.
6. Constipation
A sluggish thyroid slows digestion and bowel movement. Persistent constipation that does not respond to diet changes is a recognised symptom of hypothyroidism.
7. Depression and low mood
Thyroid hormones influence brain chemistry and mood regulation. Hypothyroidism is associated with depression, low motivation, and emotional flatness that may not respond fully to antidepressants without treating the thyroid.
8. Poor memory and brain fog
Difficulty concentrating, slow thinking, and forgetfulness are common complaints in hypothyroidism. Patients sometimes describe a feeling of mental slowness or "brain fog" that affects daily tasks.
9. Puffy face
A characteristic puffiness around the face, especially the eyes, can develop in hypothyroidism due to accumulation of fluid in tissues. This is called myxoedema and reflects severe or prolonged underactivity.
10. Heavy or irregular menstrual periods
Thyroid hormones influence the menstrual cycle. Hypothyroidism can cause heavier, more prolonged, or irregular periods, and in severe cases may contribute to subfertility.
Hyperthyroidism
10 symptoms of hyperthyroidism (overactive thyroid)
When thyroid hormone levels are too high, metabolism speeds up. Symptoms are often more acute and noticeable, and can be mistaken for anxiety or cardiac problems.
1. Unintentional weight loss
A fast metabolism burns more calories than the body takes in. Unexplained weight loss — even with a normal or increased appetite — is a hallmark feature of an overactive thyroid.
2. Palpitations
An overactive thyroid stimulates the heart, causing an awareness of the heartbeat, fluttering sensations in the chest, or irregular heartbeats. This can be alarming and may be mistaken for a cardiac condition.
3. Fast heartbeat (tachycardia)
A resting heart rate above 100 beats per minute is common in hyperthyroidism. In some people, an irregular heart rhythm called atrial fibrillation can develop, particularly in older adults.
4. Heat intolerance
Excessive thyroid hormone increases metabolic heat production. People with hyperthyroidism often feel uncomfortably hot in normal temperatures and dislike warm environments.
5. Excessive sweating
The body tries to cool down by sweating more. People with an overactive thyroid may sweat heavily even at rest, with warm and moist skin that is noticeable to others.
6. Anxiety and nervousness
High thyroid hormone levels have a stimulating effect on the nervous system, causing feelings of anxiety, irritability, restlessness, and difficulty staying calm. This is sometimes mistaken for a primary anxiety disorder.
7. Tremors
Fine trembling of the hands and fingers is a classic sign of hyperthyroidism. It results from the nervous system being overstimulated by excess thyroid hormone.
8. Insomnia
The overstimulated nervous system makes it difficult to fall asleep or stay asleep. Insomnia combined with anxiety and palpitations is a characteristic cluster of hyperthyroid symptoms.
9. Frequent bowel motions
Excess thyroid hormone speeds up intestinal movement. This can lead to frequent loose stools or diarrhoea, contrasting with the constipation seen in hypothyroidism.
10. Eye changes (Graves' eye disease)
In Graves' disease (the most common cause of hyperthyroidism), the immune system can also attack the tissue behind the eyes, causing them to bulge (proptosis), appear wide and staring, or become red and irritated. This is called Graves' ophthalmopathy and requires specialist assessment.
Comparison
Hypothyroidism vs hyperthyroidism: quick comparison
The two conditions often produce opposite symptoms because one slows the body down and the other speeds it up.
| Symptom area | Hypothyroidism (underactive) | Hyperthyroidism (overactive) |
|---|---|---|
| Weight | Weight gain | Weight loss |
| Temperature | Cold intolerance, feeling cold | Heat intolerance, excessive sweating |
| Heart rate | Slow pulse (bradycardia) | Fast pulse (tachycardia), palpitations |
| Bowel habit | Constipation | Frequent bowel motions, diarrhoea |
| Energy | Fatigue, tiredness | Restlessness, insomnia |
| Mood | Depression, low mood | Anxiety, irritability, nervousness |
| Skin and hair | Dry skin, hair loss, brittle nails | Fine hair, warm moist skin |
| Menstrual cycle | Heavy or irregular periods | Light or absent periods |
| Cognition | Brain fog, poor memory | Difficulty concentrating due to anxiety |
Key point: Many of these symptoms overlap with other common conditions. A simple blood test — the TSH — is the most important first step in ruling out thyroid disease when these symptoms are present.
Diagnosis
Which tests are used to diagnose thyroid disease?
If thyroid disease is suspected based on symptoms, your doctor will request one or more blood tests and occasionally an imaging scan.
- TSH (Thyroid Stimulating Hormone): The first and most important test. TSH is produced by the pituitary gland to control thyroid activity. An abnormal TSH is the earliest and most sensitive indicator of thyroid dysfunction.
- Free T4 (Free Thyroxine): Measures the active form of the main thyroid hormone. Used together with TSH to confirm hypothyroidism or hyperthyroidism.
- Free T3 (Free Triiodothyronine): The active form of the other thyroid hormone. Measured when T3 toxicosis is suspected or to monitor hyperthyroidism treatment.
- Thyroid antibodies (TPO and TgAb): Used to identify autoimmune thyroid disease such as Hashimoto's thyroiditis (causing hypothyroidism) or Graves' disease (causing hyperthyroidism).
- Thyroid ultrasound: An imaging scan to assess the size, shape, and structure of the thyroid gland. Useful when a goitre or nodule is felt or suspected on examination.
In most cases, the TSH alone is enough to screen for thyroid disease. Your doctor will decide which additional tests are needed based on your result and clinical picture.
To understand your thyroid blood test results, use our Thyroid Report Reader tool.
Interpreting results
How is TSH interpreted?
The TSH result works in the opposite direction to what most people expect — because TSH rises when the pituitary gland is trying to stimulate a sluggish thyroid.
| TSH result | Most likely meaning | Next step |
|---|---|---|
| TSH high (above reference range) | Hypothyroidism (underactive thyroid) | Free T4 is measured to confirm |
| TSH normal | Thyroid is likely functioning normally | Review other possible causes of symptoms |
| TSH low (below reference range) | Hyperthyroidism (overactive thyroid) | Free T4 and Free T3 are measured to confirm |
| TSH borderline high with normal T4 | Subclinical hypothyroidism | Monitoring with repeat testing; treatment depends on symptoms and antibody status |
Normal TSH range: Most laboratories use a reference range of approximately 0.4 to 4.0 mIU/L, but this varies by age and laboratory. Always interpret TSH results alongside your symptoms and with your doctor's guidance. A single borderline result does not always mean treatment is needed.
Read next: Use our Thyroid Report Reader to check your TSH, Free T4, and Free T3 results and understand what they mean. If you are concerned about fertility or menstrual irregularity, also see the Subfertility Screening Tool.
FAQ
Frequently Asked Questions
Yes. Hypothyroidism (underactive thyroid) commonly causes weight gain because a slow thyroid reduces metabolism. Hyperthyroidism causes weight loss instead. Both types of weight change should be investigated if the thyroid is suspected.
Yes. Both hypothyroidism and hyperthyroidism can cause hair thinning or hair loss. This usually improves when thyroid hormone levels return to normal with treatment.
Yes. Both underactive and overactive thyroid can interfere with the menstrual cycle and reduce fertility. Treating the thyroid condition often helps restore normal fertility. If you are planning a pregnancy and have thyroid symptoms, speak to your doctor about a TSH test before trying to conceive.
Yes. Uncontrolled thyroid disease during pregnancy can increase the risk of miscarriage, premature birth, and developmental problems in the baby. Thyroid screening is recommended in pregnancy, particularly for women with a family history of thyroid disease or previous thyroid problems.
It depends on the cause. Hypothyroidism is usually managed long-term with levothyroxine tablets, which replace the missing hormone effectively. Some causes of hyperthyroidism can be treated definitively with radioactive iodine or surgery. Autoimmune thyroid disease requires ongoing management and regular monitoring.
The normal TSH range is generally 0.4 to 4.0 mIU/L, though this varies by laboratory and age. A high TSH usually suggests hypothyroidism; a low TSH usually suggests hyperthyroidism. Your doctor will interpret the result in the context of your symptoms and other thyroid tests.
Final Takeaway from Dr. GajasingheThyroid disease is common, often missed, and very treatable. If you have unexplained fatigue, weight changes, mood problems, or hair loss, a simple TSH blood test is the right first step. Early detection makes treatment simpler and more effective.