Thyroid Disorders: Underactive, Overactive and the Symptoms People Miss
The thyroid is a small gland in the front of the neck that sets the pace of metabolism. When it runs slow, almost every system slows with it. When it runs fast, everything speeds up. Both are common, both are detectable with a simple blood test, and both are treatable.
Hypothyroidism: the gland running slow
Symptoms build gradually over months, which is exactly why they are attributed to age, stress or workload.
- Fatigue that sleep does not fix
- Weight gain of a few kilograms despite no change in diet
- Cold intolerance
- Constipation
- Dry skin and hair, hair thinning including the outer eyebrow
- Heavy or irregular periods
- Low mood, slowed thinking, poor concentration
- Puffiness around the eyes
- Hoarse voice
- Muscle aches and cramps
The commonest cause worldwide in iodine-sufficient areas is Hashimoto’s thyroiditis, an autoimmune condition. Other causes include thyroid surgery, radioiodine treatment, certain drugs such as lithium and amiodarone, and iodine deficiency.
Hyperthyroidism: the gland running fast
- Weight loss despite a good appetite
- Palpitations or a fast, irregular pulse
- Heat intolerance and excessive sweating
- Tremor of the hands
- Anxiety, irritability, restlessness
- Loose stools or more frequent bowel movements
- Difficulty sleeping
- Muscle weakness, especially in the thighs
- Eye changes in Graves’ disease – grittiness, bulging, double vision
Graves’ disease is the commonest cause; toxic nodules and thyroiditis account for most of the rest.
Reading the test results
Two numbers do most of the work.
- TSH is the pituitary’s instruction to the thyroid. It rises when the thyroid is underactive and falls when it is overactive, so it moves in the opposite direction to thyroid activity. It is the most sensitive single test.
- Free T4 measures the circulating hormone itself and confirms the picture.
Typical patterns:
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- High TSH with low free T4: overt hypothyroidism
- High TSH with normal free T4: subclinical hypothyroidism
- Low TSH with high free T4: overt hyperthyroidism
- Low TSH with normal free T4 and T3: subclinical hyperthyroidism
Antibody tests such as anti-TPO help establish an autoimmune cause and predict who will progress. Routine T3 testing adds little in hypothyroidism.
Where over-treatment creeps in
Subclinical hypothyroidism – a mildly raised TSH with normal T4 – is where most unnecessary treatment begins. A single mildly elevated TSH should be repeated after six to twelve weeks, because it commonly normalises on its own; it rises in acute illness, after recovery from illness, and with biotin supplements, which interfere with the assay.
Treatment of subclinical hypothyroidism is generally justified when TSH is persistently above about 10 mIU/L, when there are clear symptoms, when anti-TPO antibodies are positive, or in pregnancy and when planning pregnancy. For an otherwise well person with TSH of 5.5 and normal T4, monitoring is usually more appropriate than a lifelong tablet.
Treatment in practice
Hypothyroidism
Levothyroxine, once daily, is a straightforward replacement of what the body is not making. To work reliably it should be taken on an empty stomach, 30-60 minutes before food, and separated by at least four hours from calcium, iron, antacids and multivitamins. Dose is rechecked six to eight weeks after any change, then annually once stable.
Combination T4/T3 therapy and desiccated thyroid extract are widely promoted online but do not outperform levothyroxine in controlled trials.
Hyperthyroidism
Anti-thyroid drugs such as carbimazole or methimazole are usually first-line, with beta blockers for symptom relief while they take effect. Radioiodine and surgery are definitive options depending on cause, severity and patient preference. Graves’ eye disease needs specialist input, and smoking makes it substantially worse.
Thyroid and pregnancy
Untreated hypothyroidism in pregnancy is associated with miscarriage, pre-eclampsia and impaired fetal neurodevelopment. Requirements rise early – often by 25-30% in the first trimester – so women already on levothyroxine should contact their doctor as soon as pregnancy is confirmed rather than waiting for the first appointment.
When to see a doctor
- A visible lump or swelling in the neck
- Difficulty swallowing, or a hoarse voice lasting more than three weeks
- A fast or irregular heartbeat
- New eye bulging, double vision or eye pain
- Symptoms of either kind that persist despite treatment and a normal TSH, which may point elsewhere
This article is general health information. Thyroid results should be interpreted alongside symptoms by a doctor, and treatment should not be started or stopped on the basis of a single test.