Last reviewed 2026-04-23 · How we verify

Levothyroxine Pill

Levothyroxine is a synthetic thyroid hormone that replaces or supplements endogenous thyroid hormone to restore normal metabolic function.

Levothyroxine is a synthetic thyroid hormone that replaces or supplements endogenous thyroid hormone to restore normal metabolic function. Used for Hypothyroidism, Thyroid cancer suppression therapy, Myxedema coma (acute severe hypothyroidism).

At a glance

Mechanism of action

Levothyroxine (T4) is converted peripherally to the active form triiodothyronine (T3), which binds to thyroid hormone receptors in target tissues to regulate metabolism, growth, and development. It is used to treat hypothyroidism by restoring circulating thyroid hormone levels to normal physiological ranges, thereby normalizing metabolic rate and alleviating symptoms of thyroid hormone deficiency.

Approved indications

• Hypothyroidism
• Thyroid cancer suppression therapy
• Myxedema coma (acute severe hypothyroidism)

Common side effects

• Tremor
• Tachycardia
• Palpitations
• Anxiety
• Insomnia
• Heat intolerance
• Weight loss

Key clinical trials

• Levothyroxine as Adjuvant to a Hypocaloric Diet for the Treatment of Obesity. (PHASE3)
• A Randomized Controlled Trial of Thyroid Hormone Supplementation in Hemodialysis Patients (NA)
• Best Treatment for Women With Both (Polycystic Ovary Syndrome) PCOS and Subclinical Hypothyroidism (NA)
• MASLD in Primary Hypothyroidism and Efficacy of Dapaglifozin (EARLY_PHASE1)
• Energy Metabolism in Thyroidectomized Patients (PHASE2)
• Thyroxine Therapy for Recurrent Pregnancy Loss in Hypothyroid Women (PHASE3)
• The Effect of Thyroid Hormone Therapy on Muscle Mass and Function in Older Adults With Subclinical Hypothyroidism (PHASE4)
• Effect of Thyroid Hormone Replacement on Fatigability in Untreated Older Adults With Subclinical Hypothyroidism (PHASE4)

Primary sources

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