Endocrinology · ENDOCRINE_SOCIETY

Hypothyroidism in adults

ENDOCRINE_SOCIETY

Source:ATA Guidelines for the Treatment of Hypothyroidism (2014, current)ETA 2025 Guidelines on Levothyroxine Sodium Preparations

Verified Apr 2026

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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.

References

1.ATA Guidelines for the Treatment of Hypothyroidism (2014, current); ETA 2025 Guidelines on Levothyroxine Sodium Preparations (2014)

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