Understanding Symptoms of Thyroid Disease
What the thyroid does and why symptoms matter
The thyroid is a small gland in your neck that regulates metabolism, energy, temperature, heart function, digestion, and many body systems. When thyroid hormone levels are too low (hypothyroidism) or too high (hyperthyroidism), symptoms may develop gradually and can be mistaken for stress, ageing, or lifestyle changes. Recognising patterns helps you seek timely review.
Symptoms of an underactive thyroid (hypothyroidism)
Hypothyroidism occurs when the thyroid does not produce enough hormone. Symptoms may include:
fatigue or low energy
weight gain or difficulty losing weight
cold intolerance
dry skin, hair thinning, or brittle hair
constipation
heavy or irregular menstrual bleeding
low mood, brain fog, or slow thinking
slower heart rate and feeling generally “slowed down”
Symptoms often develop slowly over time.
Symptoms of an overactive thyroid (hyperthyroidism)
Hyperthyroidism occurs when the thyroid produces too much hormone. Symptoms may include:
unexplained weight loss despite normal or increased appetite
heat intolerance and sweating
palpitations or a racing heartbeat
anxiety, irritability, tremor, or restlessness
diarrhoea or frequent bowel motions
difficulty sleeping
menstrual changes
muscle weakness
Symptoms may come on gradually or occasionally more quickly.
Symptoms that may appear in either condition
Because the thyroid affects many systems, some symptoms overlap, including fatigue, mood changes, menstrual changes, and difficulty concentrating. A visible neck swelling (goitre) may occur in some thyroid conditions. Eye changes—such as redness, irritation, bulging, discomfort, or vision problems—can occur particularly in autoimmune thyroid disease.
Red Flags — Seek Urgent Review if You Experience
severe or persistent palpitations
fainting, dizziness, or chest pain
sudden, painful, or rapidly enlarging neck swelling
severe or sudden eye pain, vision loss, or rapidly worsening eye symptoms
fever and severe neck tenderness
These symptoms may suggest a condition requiring urgent assessment.
Common Myths vs Reality
“Thyroid problems always cause obvious symptoms.”
Not always. Many symptoms are subtle and develop slowly. Some people feel very unwell; others barely notice changes.
“If I gain weight, it must be my thyroid.”
Weight change can have many causes. Thyroid disease is one possibility but not the only explanation. Testing is important rather than assuming.
“If I start treatment, I’ll feel better instantly.”
Some people improve quickly, but for many, improvement is gradual and requires careful monitoring and dose adjustment.
“Eye symptoms mean something is wrong with the eyes only.”
Eye changes can be linked to certain thyroid conditions and should always be discussed with your doctor.
When to See Your GP
See your GP if you experience persistent fatigue, unexplained weight change, temperature intolerance, mood or heart rhythm changes, or a neck swelling. Thyroid disease is diagnosed with blood tests and sometimes ultrasound or specialist assessment. With appropriate treatment and monitoring, most thyroid conditions are manageable and outcomes are generally good.
This article provides general health information only and does not replace medical advice. Please speak with your GP for personalised care.