Red Flags
- Myxoedema coma — hypothermia, hypotension, hypoventilation, altered mental status with severe hypothyroidism — IV levothyroxine plus IV hydrocortisone in ICU[1]
- Newly diagnosed hypothyroidism with concurrent unrecognised adrenal insufficiency — give hydrocortisone first to avoid precipitating adrenal crisis on starting levothyroxine[1]
- Pregnancy with overt hypothyroidism — adverse maternal/fetal outcomes; immediate levothyroxine, target TSH <2.5 in 1st trimester, <3.0 thereafter[1]
- Symptomatic angina or arrhythmia in elderly starting levothyroxine — start low (12.5–25 mcg) and titrate slowly to avoid precipitating ischaemia[1]
First-line treatment
Interventions
- Subclinical hypothyroidism management[1]Treat if TSH ≥10 mIU/L, pregnancy or planning pregnancy, infertility, or symptomatic with TSH 4.5–10 plus positive anti-TPO. Otherwise observation with TSH every 6–12 months
- Annual TSH monitoring once stable[1]Once euthyroid on stable LT4 dose, check TSH annually; sooner with weight change ≥10%, pregnancy, new medications affecting absorption (PPIs, calcium, iron)
First-line drug therapy
| Drug | Class | Adult | Paediatric | Notes |
|---|---|---|---|---|
| Levothyroxine (LT4)[1] | Synthetic thyroid hormone (T4) | 1.6 mcg/kg/day PO once daily on empty stomach (typically 100–125 mcg). Lower starting dose (12.5–50 mcg) in elderly, CAD, frail; titrate every 4–6 weeks by 12.5–25 mcg per TSH | 10–15 mcg/kg/day in neonates with congenital hypothyroidism; weight-based per age in older children | Take 30–60 minutes before food, separated from calcium, iron, PPIs, sucralfate by 4 hours |
| Levothyroxine in pregnancy[1] | Thyroid hormone (T4) — pregnancy adjusted | Increase pre-pregnancy dose by 25–30% on confirmation of pregnancy; monitor TSH every 4 weeks in 1st half then every 4–6 weeks | — | Target TSH <2.5 mIU/L in 1st trimester, <3.0 thereafter. Postpartum return to pre-pregnancy dose |
| Liothyronine (LT3)[1] | Synthetic thyroid hormone (T3) | Combination with LT4 — 5–25 mcg LT3 daily plus reduced LT4; reserve for selected patients with persistent symptoms despite normal TSH on LT4 monotherapy | — | Most patients do well on LT4 alone; T3 combination is not first-line. Monitor for arrhythmia, anxiety, osteoporosis |
Levothyroxine (LT4)[1]
Synthetic thyroid hormone (T4)
- Adult
- 1.6 mcg/kg/day PO once daily on empty stomach (typically 100–125 mcg). Lower starting dose (12.5–50 mcg) in elderly, CAD, frail; titrate every 4–6 weeks by 12.5–25 mcg per TSH
- Paediatric
- 10–15 mcg/kg/day in neonates with congenital hypothyroidism; weight-based per age in older children
Take 30–60 minutes before food, separated from calcium, iron, PPIs, sucralfate by 4 hours
Levothyroxine in pregnancy[1]
Thyroid hormone (T4) — pregnancy adjusted
- Adult
- Increase pre-pregnancy dose by 25–30% on confirmation of pregnancy; monitor TSH every 4 weeks in 1st half then every 4–6 weeks
- Paediatric
- —
Target TSH <2.5 mIU/L in 1st trimester, <3.0 thereafter. Postpartum return to pre-pregnancy dose
Liothyronine (LT3)[1]
Synthetic thyroid hormone (T3)
- Adult
- Combination with LT4 — 5–25 mcg LT3 daily plus reduced LT4; reserve for selected patients with persistent symptoms despite normal TSH on LT4 monotherapy
- Paediatric
- —
Most patients do well on LT4 alone; T3 combination is not first-line. Monitor for arrhythmia, anxiety, osteoporosis
Safety-net
- Take levothyroxine on an empty stomach 30–60 minutes before food, with water only — calcium, iron, coffee, soy, and PPIs reduce absorption[1]
- Do not stop levothyroxine — hypothyroidism rebounds within weeks; pregnancy especially needs continuous treatment[1]
- If you become pregnant, contact your clinician same week — most women need a 25–30% dose increase on confirmation[1]
Referral criteria
- Suspected myxoedema comaEmergency department / ICU; IV levothyroxine plus IV hydrocortisone[1]
- Pregnancy with hypothyroidismEndocrinology and obstetric medicine — joint care[1]
- Persistent symptoms despite normal TSH on adequate LT4 doseEndocrinology to consider combination LT4/LT3 trial or alternative diagnoses[1]
- Suspected central (secondary) hypothyroidism (low TSH and low free T4)Endocrinology for pituitary workup[1]
Clinical summary
Diagnosis and treatment of overt and subclinical hypothyroidism with weight-based levothyroxine titrated to normal TSH; combination therapy reserved for select cases.