Thyroid Hormones

Endocrine & Metabolic

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Examples

levothyroxine (Synthroid)liothyronine

Prefix / Suffix: lev-/lio-

Physiology

Thyroid hormones (T3, T4) regulate metabolism, growth, and energy. Hypothyroidism causes fatigue, weight gain, and cold intolerance.

Mechanism of Action

Synthetic form of T4 (levothyroxine) or T3 (liothyronine) — replaces deficient thyroid hormone, restoring normal metabolic function.

Indications

Hypothyroidism (Hashimoto's, post-thyroidectomy)
Myxedema coma (IV liothyronine)
TSH suppression in thyroid cancer

Side Effects / Adverse Effects

Signs of hyperthyroidism if overdosed: tachycardia, palpitations, weight loss, heat intolerance, tremor
Atrial fibrillation, especially in elderly
Osteoporosis (long-term over-replacement)
Insomnia

Contraindications

Untreated adrenal insufficiency
Acute MI
Thyrotoxicosis

Nursing Considerations

Take on empty stomach, 30–60 min before breakfast (consistent absorption)
Avoid taking with calcium, iron, antacids, soy (decrease absorption — separate by 4 hours)
Lifelong therapy in most cases — never stop abruptly
Monitor TSH every 6–8 weeks after dose changes, then yearly
Start low and titrate slowly in elderly and cardiac patients
Teach signs of over-replacement (hyperthyroid symptoms)
Effects take 4–6 weeks to be fully apparent

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Disclaimer: PharmPal Nurse is for education only and is not medical advice. Do not use it to diagnose, treat, prescribe, or make patient-care decisions; always verify with current drug references, your instructor, facility policy, and a licensed provider. In emergencies, call local emergency services.