Hypothyroidism
An underactive thyroid causing fatigue, weight gain and cold intolerance.
Overview
Hypothyroidism is most often autoimmune (Hashimoto's). It is treated with levothyroxine titrated to a normal TSH. Symptoms can take weeks to improve after starting treatment.
Symptoms
- • Fatigue
- • Weight gain
- • Cold intolerance
- • Dry skin and hair
- • Constipation
- • Low mood
- • Menstrual changes
Risk factors
- • Female sex
- • Age >60
- • Family history of autoimmune disease
- • Previous thyroid surgery or radioiodine
- • Type 1 diabetes
Causes
- • Autoimmune thyroiditis
- • Iodine deficiency
- • Post-treatment of hyperthyroidism
- • Certain medications (amiodarone, lithium)
🚨 Red flags — seek urgent care
- • Severe lethargy with low temperature or confusion (myxoedema)
- • Heart failure symptoms
When to seek care
- • Persistent fatigue with classical features
- • Annual review while on levothyroxine
Diagnosis
- • TSH elevated with low free T4 = primary hypothyroidism (commonest)
- • Subclinical: raised TSH with normal free T4 — treat if TSH >10 mU/L, symptomatic, or fertility/pregnancy planning
- • Check thyroid peroxidase antibodies (TPO) for autoimmune (Hashimoto) cause
- • Consider central hypothyroidism if both TSH and free T4 are low
Treatment
- • Levothyroxine — start 1.6 mcg/kg/day (lower in elderly or cardiac disease, e.g. 25–50 mcg)
- • Take fasting, ≥30 min before food, separate from calcium/iron
- • Recheck TSH 6–8 weeks after initiation or dose change; target TSH 0.5–2.5 mU/L in symptomatic patients
- • Increase dose by ~25% in pregnancy as soon as confirmed
- • Combination T3 only in specialist clinics for selected symptomatic patients
Prevention
- • Adequate dietary iodine (especially in pregnancy)
- • Avoid excessive selenium / iodine supplementation without indication
- • Postpartum thyroid screening for at-risk women
Complications
- • Myxoedema coma (rare medical emergency)
- • Adverse pregnancy outcomes (miscarriage, pre-eclampsia, neurodevelopmental impact)
- • Dyslipidaemia and cardiovascular risk
- • Depression and cognitive impairment
Education & self-care
This guidance is reviewed by Dr. Handel Emery, MD, FRCP (UK) and last updated 2026-06-08. It is educational and not a substitute for professional medical advice.
Frequently asked questions
Will I need treatment for life?
Most people with autoimmune hypothyroidism need lifelong levothyroxine, with periodic dose adjustment.
Why must levothyroxine be taken on an empty stomach?
Food, coffee, calcium and iron tablets all reduce levothyroxine absorption by up to half. Take it 30–60 minutes before breakfast or at bedtime, 4 hours after any interacting supplement.
How often is monitoring needed?
After dose changes, recheck TSH at 6–8 weeks. Once stable, an annual TSH is usually sufficient. Aim for TSH in the lower half of the reference range in most adults.
Will I need levothyroxine for life?
For most causes (autoimmune Hashimoto's, post-surgical, post-radioactive iodine) — yes. Transient thyroiditis-related hypothyroidism may resolve and allow medication to be stopped under specialist guidance.