Last reviewed 2026-04-20 · How we verify

Unithroid (LEVOTHYROXINE SODIUM)

Unithroid works by replacing or supplementing the thyroid hormone thyroxine, which is produced by the thyroid gland.

Unithroid (Levothyroxine Sodium) is a synthetic thyroid hormone medication developed by Stevens J and currently owned by Fresenius Kabi USA. It targets the thyroid hormone receptor beta and belongs to the l-Thyroxine class of small molecules. Unithroid is FDA-approved for various thyroid-related conditions, including hypothyroidism, goiter, and hyperlipidemia. The medication is available as a generic product from multiple manufacturers, indicating it is off-patent. Key safety considerations include monitoring thyroid hormone levels and potential interactions with other medications.

At a glance

Mechanism of action

Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins.The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.

Approved indications

• Congenital hypothyroidism
• Diagnostic Test for Thyroid Dysfunction
• Goiter
• Hashimoto thyroiditis
• Hyperlipidemia
• Hypothyroidism
• Malignant tumor of thyroid gland
• Myxedema

Boxed warnings

• WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS Thyroid hormones, including UNITHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects [see Adverse Reactions ( 6 ), Drug Interactions ( 7.7 ), and Overdosage ( 10 )] . WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS See full prescribing information for complete boxed warning. Thyroid hormones, including UNITHROID, should not be used for the treatment of obesity or for weight loss. Doses beyond the range of daily hormonal requirements may produce serious or even life threatening manifestations of toxicity ( 6 , 10 ).

Common side effects

• Weight loss
• Hair loss
• Diarrhea
• Vomiting
• Abdominal cramps
• Palpitations
• Tachycardia
• Arrhythmias
• Increased pulse and blood pressure
• Heart failure
• Angina
• Myocardial infarction

Drug interactions

• ferric sulfate
• phenprocoumon
• sucralfate
• warfarin

Key clinical trials

• Novel Approaches to the Treatment of Hypothyroidism (PHASE2,PHASE3)
• Comparison of Levothyroxine Formulations in the Treatment of Congenital Hypothyroidism
• T4/T3 Therapy in Hypothyroidism (PHASE2)
• SNUH Immune Checkpoint Inhibitor-induced Hypothyroidism Recovery Trial (NA)
• Thyroid Hormone for Treatment of Nonalcoholic Steatohepatitis in Veterans (PHASE2)
• Dosing of LT4 in Older Individuals (PHASE4)
• A Study Evaluation the Safety and Efficacy of Hormone Replacement Therapy With North Star Compared to Levothyroxine in Patients With Primary Hypothyroidism (PHASE2)
• Precision Medicine Approach for Early Dementia & Mild Cognitive Impairment (PHASE3)

Patents

Primary sources

Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.

Competitive intelligence

For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:

• Unithroid CI brief — competitive landscape report
• Unithroid updates RSS · CI watch RSS
• Fresenius Kabi portfolio CI