In brief: Your thyroid gland regulates metabolism. Underactive thyroid (hypothyroidism) slows the body—causing fatigue, weight gain, and cold intolerance. Overactive thyroid (hyperthyroidism) speeds things up—causing weight loss, rapid heartbeat, and anxiety. Symptoms overlap with stress, anaemia, and menopause, so blood tests (TSH, free T4) are essential. Treatment is effective for most people once diagnosed.
Hypothyroidism (underactive thyroid)
- Fatigue, weight gain, feeling cold
- Dry skin, hair thinning, constipation
- Depression, slowed thinking, heavy periods
- Raised cholesterol in some people
Hypothyroidism can contribute to chronic fatigue and is checked alongside iron deficiency.
Hyperthyroidism (overactive thyroid)
- Unintended weight loss, heat intolerance, sweating
- Rapid or irregular heartbeat, anxiety, tremor
- Loose stools, difficulty sleeping
- Eye changes in Graves' disease
Diagnosis
TSH is the usual first test, with free T4 and sometimes T3 or thyroid antibodies. One abnormal result should be confirmed. Thyroid ultrasound may evaluate nodules; fine-needle biopsy is used when cancer is suspected. See our blood test guide for how TSH fits into routine panels.
Treatment overview
- Hypothyroidism — levothyroxine with dose adjusted by periodic blood tests
- Hyperthyroidism — antithyroid drugs, radioactive iodine, or surgery depending on cause
- Nodules — surveillance or specialist referral based on ultrasound features
Frequently asked questions
What TSH level is normal?
Most labs use roughly 0.4–4.0 mIU/L, but targets on treatment may differ (often 0.5–2.5 for hypothyroidism). Pregnancy has special ranges.
Can thyroid problems cause weight change?
Yes—hypothyroidism associates with weight gain; hyperthyroidism with loss. Diet and exercise still matter; medicines normalise hormone levels over weeks to months.
Do I need a thyroid ultrasound?
Not for every patient. Ultrasound helps when your clinician feels a nodule, or symptoms suggest structural disease.
Is thyroid disease autoimmune?
Often yes—Hashimoto's (hypo) and Graves' (hyper) are common autoimmune thyroid conditions. Antibody tests may support diagnosis.
Questions to ask your doctor
- Could my symptoms be thyroid-related rather than depression or ageing?
- What TSH target should I aim for on treatment?
- Do I need antibody tests or a thyroid ultrasound?
- How often should we recheck levels?
- When should I see an endocrinologist?
Trusted references
- WHO — Iodine and thyroid health
- NHS — Underactive thyroid
- American Thyroid Association
- NIH NIDDK — Endocrine diseases
Find a clinician on DoctorBookly
If you have symptoms or risk factors discussed here, book a consultation with a verified doctor, visit a hospital, or arrange lab tests near you. Early assessment matters.
Educational content from DoctorBookly Editorial. Not personal medical advice. Always consult a licensed clinician for diagnosis, treatment, and emergencies. Call your local emergency number if you think you are having a medical emergency.
