Thyroid problems: symptoms of an over or underactive thyroid

The thyroid is a small butterfly-shaped gland sitting at the base of the neck, and it produces two hormones (thyroxine and triiodothyronine) that regulate the pace of almost every tissue in the body.

When it produces too little, everything slows down; when it produces too much, everything races.

Around one in twenty adults in the United Kingdom lives with a thyroid condition, and women are roughly eight times more likely to be affected than men.

This article walks through the symptoms that matter, the blood tests your GP will use, and the treatments currently recommended in British practice.

How the thyroid works

The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH). TSH then drives the thyroid to produce thyroxine (T4) and a smaller amount of triiodothyronine (T3). T4 is the storage form; in peripheral tissues it is converted to T3, which is the biologically active hormone. A negative feedback loop means that if T4 and T3 fall, TSH rises to stimulate more production, and if they rise, TSH falls. This is why TSH is the most sensitive first-line blood test in most situations. The British Thyroid Foundation has excellent patient-friendly resources on this physiology.

Hypothyroidism: when the thyroid is underactive

Hypothyroidism affects around 2 to 5% of British women and closer to 0.5% of men.

The commonest cause is autoimmune (Hashimoto's) thyroiditis, in which circulating autoantibodies (TPO and sometimes thyroglobulin antibodies) progressively destroy thyroid follicles.

Other causes include previous radioactive iodine treatment, thyroid surgery, lithium or amiodarone therapy, congenital hypothyroidism (now screened for in newborns via the NHS blood spot), and, worldwide, iodine deficiency.

Symptoms to look for

• Persistent fatigue and daytime sleepiness out of keeping with your actual workload.
• Weight gain despite no change in eating patterns, often with fluid retention.
• Cold intolerance, needing extra layers when others are comfortable.
• Constipation.
• Dry skin, coarse hair, brittle nails, hair loss (especially the outer third of the eyebrows).
• Muscle aches and cramps, slowed reflexes.
• Low mood, poor concentration, memory lapses.
• Menstrual changes: heavy or irregular periods, subfertility.
• Hoarse voice, a puffy face, slow heart rate in advanced disease.

Many of these symptoms are non-specific, which is why thyroid blood tests are frequently included in the routine workup of persistent tiredness, mood changes or unexplained weight change. The NHS underactive thyroid page lists the same features and describes the diagnostic pathway.

How it is diagnosed

The first-line test is TSH. If TSH is raised (usually above 4.5 to 5 mU/L, depending on local reference range) and free T4 is below the reference range, this is overt hypothyroidism, and treatment is recommended. If TSH is raised but free T4 is still within range, this is subclinical hypothyroidism. The BNF thyroid disorders summary and NICE guidance recommend considering treatment if TSH is above 10 mU/L, or if TSH is between the upper limit of normal and 10 mU/L with significant symptoms, or in pregnancy and planned pregnancy.

How it is treated

The treatment of choice is levothyroxine, a synthetic form of T4. The usual starting dose in otherwise healthy adults is 1.6 micrograms per kilogram per day, rounded to a standard tablet strength (typically 50 to 100 micrograms daily). Older patients, patients with cardiovascular disease, and long-standing severe hypothyroidism start lower (25 to 50 micrograms) and titrate upwards every four to six weeks based on TSH. Swallow the tablet on an empty stomach with water, at least thirty minutes before food, coffee or other medicines, especially calcium, iron, indigestion remedies and proton pump inhibitors, which all reduce absorption.

Once stable, TSH is rechecked yearly. Pregnancy increases thyroxine requirement by around 25 to 50%, and dose is usually raised as soon as pregnancy is confirmed, with close monitoring. Combination T3/T4 therapy and desiccated thyroid extract are not routinely recommended in NHS practice; a minority of patients with persistent symptoms despite biochemical correction are referred to endocrinology for consideration of liothyronine under specialist supervision. A wider view of endocrine-system treatments and the overlap with women's health is worth reading for anyone planning pregnancy or managing menopausal symptoms alongside a thyroid diagnosis.

Hyperthyroidism: when the thyroid is overactive

Hyperthyroidism affects around 1 in 100 British women and is most often caused by Graves' disease, an autoimmune condition in which antibodies (TSH-receptor antibodies) stimulate the thyroid to over-produce hormone. Other causes include toxic multinodular goitre, a single toxic adenoma, thyroiditis (post-viral, post-partum, silent), and overtreatment with levothyroxine. Amiodarone and iodinated contrast agents can also precipitate it.

Symptoms to look for

• Unintentional weight loss despite a good appetite.
• Heat intolerance, sweating, warm moist skin.
• Palpitations, a fast or irregular pulse (atrial fibrillation is more common with age).
• Tremor of the hands, restlessness, anxiety and irritability.
• Frequent loose stools.
• Fatigue despite feeling wired.
• Menstrual irregularity, lighter or absent periods.
• Eye changes in Graves' disease: lid retraction, proptosis, dry or gritty eyes, double vision.
• A smooth, diffusely enlarged goitre (Graves') or a lumpy irregular gland (toxic nodular disease).

Untreated severe hyperthyroidism can tip into thyroid storm, with high fever, severe tachycardia and confusion, which is a medical emergency requiring hospital care.

How it is diagnosed

TSH is suppressed (usually below 0.1 mU/L) and free T4 and/or free T3 are raised.

Further work-up includes TSH-receptor antibodies (to confirm Graves'), TPO antibodies, thyroid ultrasound if there is a nodular goitre, and in some cases a radioisotope uptake scan to distinguish Graves' from thyroiditis.

How it is treated

Three options exist in the UK: antithyroid drugs (carbimazole first-line, propylthiouracil reserved mainly for the first trimester of pregnancy or carbimazole-intolerant patients), radioactive iodine, and thyroidectomy. Antithyroid drugs are usually tried first in Graves' disease, either as block-and-replace or a titration regimen, for twelve to eighteen months. Beta-blockers, most commonly propranolol, are used alongside to control palpitations, tremor and anxiety while the antithyroid drug takes effect, typically over four to six weeks.

After one course of antithyroid drugs, around half of patients achieve long-term remission. The remainder, and patients with toxic nodular disease, are usually offered radioactive iodine (a single oral capsule at a specialist centre) or surgical thyroidectomy. Both definitive options typically produce hypothyroidism, which is then treated with levothyroxine for life. All options and their overlap with thyroid disorders treatments are discussed in our treatment hub.

Thyroid eye disease

Graves' orbitopathy (thyroid eye disease) affects a quarter to a half of patients with Graves' disease.

Smoking dramatically worsens it, and stopping smoking is the single most effective self-help measure.

Mild cases are treated with tear substitutes and selenium; moderate-to-severe cases need referral to a combined endocrinology-ophthalmology clinic, where intravenous glucocorticoids or newer targeted therapies (teprotumumab where available) may be used.

Frequently asked questions

Can thyroid problems run in families?

Yes. Autoimmune thyroid disease clusters in families and also clusters with type 1 diabetes, coeliac disease, pernicious anaemia and vitiligo. A first-degree relative with a thyroid disorder lowers the threshold for testing.

Is it safe to get pregnant with a thyroid condition?

Yes, provided it is well controlled. Hypothyroid women usually need a higher levothyroxine dose in pregnancy, and hyperthyroid women need careful specialist management. Pre-conception review is strongly recommended.

Does iodine in the diet matter?

Mild iodine deficiency is making a comeback in the UK, particularly in women who avoid dairy.

Aim for adequate dietary iodine (dairy, white fish, eggs), but do not take high-dose iodine supplements without medical advice, as they can precipitate thyroid dysfunction.

Can stress cause thyroid disease?

Stress does not cause autoimmune thyroid disease, but it can unmask symptoms or precipitate flares. Managing sleep, exercise and workload helps overall wellbeing.

Do I need an ultrasound for every thyroid problem?

No. Ultrasound is indicated for a palpable nodule, an irregular goitre, or suspicion of malignancy. Uncomplicated autoimmune hypothyroidism without a palpable abnormality does not routinely need imaging.

Subclinical thyroid disease: a grey zone worth understanding

Subclinical hypothyroidism (raised TSH with normal free T4) and subclinical hyperthyroidism (suppressed TSH with normal free T4 and free T3) are common incidental findings on blood tests.

The NICE position is pragmatic: treat subclinical hypothyroidism if TSH is persistently above 10 mU/L, or between 4 to 10 mU/L with significant symptoms, during pregnancy or when trying to conceive.

Treat subclinical hyperthyroidism if TSH is persistently below 0.1 mU/L, particularly in older adults, post-menopausal women at risk of osteoporosis, and anyone with atrial fibrillation.

Where the case for treatment is borderline, repeating thyroid function tests in six to twelve weeks, alongside thyroid antibodies, usually clarifies the direction of travel.

Practical advice on taking levothyroxine well

Levothyroxine is one of the most commonly prescribed medicines in the NHS, yet absorption issues account for a large share of suboptimal control.

Take it on waking with a full glass of water, then wait at least thirty (ideally sixty) minutes before food, coffee or tea.

Separate calcium carbonate, iron, magnesium, proton pump inhibitors, colestyramine, soy products and high-fibre breakfasts by four hours.

If mornings are impossible, a bedtime dose at least three hours after the last food is a reasonable alternative and is often better tolerated.

Consistency of brand matters; if the pharmacy substitutes a different manufacturer, TSH sometimes drifts and a recheck six weeks after any switch is sensible.

Missed doses: if you remember the same day, take it; if the next morning, take the missed dose and the usual dose together, since the half-life of levothyroxine is about a week.

Sustained missed doses will raise TSH within two to three weeks.

Thyroid nodules: how worried should I be?

Palpable or ultrasound-detected thyroid nodules are extremely common, affecting up to half of women by the age of sixty.

The vast majority are benign, but a small minority (around 5%) are malignant, and the role of primary care is triage rather than deep investigation.

A nodule with any worrying feature (rapid growth, hoarseness, lymphadenopathy, hard fixed texture, family history of medullary thyroid cancer or MEN syndromes) warrants a two-week-wait referral to head and neck or endocrine surgery.

Otherwise, an ultrasound (U-score) and fine-needle aspiration where indicated (Thy grading) sort benign from suspicious nodules.

The British Thyroid Association thyroid cancer guidelines set out this pathway in detail.

Hashimoto's thyroiditis and coexisting autoimmunity

Hashimoto's rarely travels alone.

Clinicians routinely screen for coeliac disease (tissue transglutaminase), type 1 diabetes (HbA1c), pernicious anaemia (B12, intrinsic factor antibodies) and, if skin changes are present, vitiligo.

The same is true of Graves' disease. When multiple autoimmune conditions stack up, the label of autoimmune polyendocrine syndrome may be used, and endocrinology input is appropriate.

Conclusion

Thyroid disorders are common, treatable, and often transform how a person feels within weeks of starting the right medication. Persistent fatigue, weight change that does not fit your lifestyle, palpitations, heat or cold intolerance, mood changes and menstrual disturbance all justify a simple blood test. Levothyroxine for hypothyroidism, carbimazole with or without propranolol for hyperthyroidism, and timely referral for radioactive iodine or surgery when needed together cover the majority of British cases. If you are pregnant, planning pregnancy, or have eye symptoms alongside thyroid disease, ask early for specialist input.

This article is for information only and does not replace personal medical advice. Discuss any symptoms or changes to treatment with your GP or endocrinologist.