Levothyroxine Side Effects: Common, Serious & FDA Warnings
Based on 308,000+ FDA adverse event reports, the most-reported levothyroxine reactions include fatigue, nausea, and headache. No active recalls are on record. The FDA-approved label carries a boxed warning.
WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS Thyroid hormones, including levothyroxine sodium, 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 levothyroxine sodium, 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 of Levothyroxine
The most-reported reactions in the FDA Adverse Event Reporting System (FAERS) for levothyroxine. Percentages reflect the share of reports mentioning each reaction; a single report may include multiple reactions. Reports indicate co-occurrence, not causation.
| Reaction | Reports | % of total |
|---|---|---|
| Fatigue | 26,243 | 8.5% |
| Nausea | 22,331 | 7.2% |
| Headache | 19,114 | 6.2% |
| Diarrhoea | 18,462 | 6.0% |
| Dyspnoea | 16,478 | 5.3% |
| Pain | 16,161 | 5.2% |
| Dizziness | 15,616 | 5.1% |
| Arthralgia | 13,171 | 4.3% |
| Asthenia | 13,354 | 4.3% |
| Malaise | 12,292 | 4.0% |
Serious Outcomes and FDA Warnings
FAERS reports flagged with a serious outcome (death, hospitalization, life-threatening, disability, or congenital anomaly), plus reactions surfaced in the FDA-approved label's Warnings section. Reports indicate co-occurrence, not causation.
| Outcome flag | Reports | % of total |
|---|---|---|
| Serious reports (any flag) | — | — |
| Hospitalization | — | — |
From the FDA-approved label, Section 5.1: Serious Risks Related to Overtreatment or Undertreatment with Levothyroxine Sodium Tablets
Levothyroxine sodium tablets has a narrow therapeutic index. Overtreatment or undertreatment with levothyroxine sodium tablets may have negative effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, gastrointestinal function, and glucose and lipid metabolism in adult or pediatric patients. In pediatric patients with congenital and acquired hypothyroidism, undertreatment may adversely affect cognitive development and linear growth, and overtreatment is associated with craniosynostosis and acceleration of bone age [Use in Specific Populations (8.4) ].Show full Section 5.1
Titrate the dose of levothyroxine sodium tablets carefully and monitor response to titration to avoid these effects [see Dosage and Administration (2.4)]. Consider the potential for food or drug interactions and adjust the administration or dosage of levothyroxine sodium tablets as needed [see Dosage and Administration (2.1) , Drug Interactions (7.1) , and Clinical Pharmacology (12.3) ].
From the FDA-approved label, Section 5.4: Acute Adrenal Crisis in Patients with Concomitant Adrenal Insufficiency
Thyroid hormone increases metabolic clearance of glucocorticoids. Initiation of thyroid hormone therapy prior to initiating glucocorticoid therapy may precipitate an acute adrenal crisis in patients with adrenal insufficiency. Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with levothyroxine sodium [see Contraindications (4) ] .
Levothyroxine Recalls
FDA enforcement actions matched to levothyroxine via openFDA's structured generic_name field and the NDC bridge. Ongoing recalls are listed below (verify on FDA →).
No recalls are on record for this drug in the FDA enforcement database.
Levothyroxine Shortages
FDA-listed shortages of levothyroxine products. Strength and dosage-form level detail.
| Strength | Reason | Resolved | Status |
|---|---|---|---|
| Euthyrox, Tablet, 25 ug (NDC 72305-025-90) | — | — | Discontinued |
| Euthyrox, Tablet, 50 ug (NDC 72305-050-30) | — | — | Discontinued |
| Euthyrox, Tablet, 88 ug (NDC 72305-088-30) | — | — | Discontinued |
| Euthyrox, Tablet, 150 ug (NDC 72305-150-30) | — | — | Discontinued |
| Euthyrox, Tablet, 125 ug (NDC 72305-125-30) | — | — | Discontinued |
| Euthyrox, Tablet, 50 ug (NDC 72305-050-90) | — | — | Discontinued |
| Euthyrox, Tablet, 125 ug (NDC 72305-125-90) | — | — | Discontinued |
| Euthyrox, Tablet, 150 ug (NDC 72305-150-90) | — | — | Discontinued |
| Euthyrox, Tablet, 25 ug (NDC 72305-025-30) | — | — | Discontinued |
| Euthyrox, Tablet, 88 ug (NDC 72305-088-90) | — | — | Discontinued |
Is Levothyroxine Safe?
Levothyroxine is FDA-approved. The label's Warnings and Precautions section covers serious risks related to overtreatment or undertreatment with levothyroxine sodium tablets (Section 5.1), cardiac adverse reactions in the elderly and in patients with underlying cardiovascular disease (Section 5.2), myxedema coma (Section 5.3), acute adrenal crisis in patients with concomitant adrenal insufficiency (Section 5.4), worsening of diabetic control (Section 5.5), decreased bone mineral density associated with thyroid hormone over-replacement (Section 5.6), risk of allergic reactions due to tartrazine (Section 5.7), serious risks related to overtreatment or undertreatment with levothyroxine sodium tablets (Section 5.1), cardiac adverse reactions in the elderly and in patients with underlying cardiovascular disease (Section 5.2), myxedema coma (Section 5.3), acute adrenal crisis in patients with concomitant adrenal insufficiency (Section 5.4), worsening of diabetic control (Section 5.5), decreased bone mineral density associated with thyroid hormone over-replacement (Section 5.6), risk of allergic reactions due to tartrazine (Section 5.7).
As with any prescription, the assessment of safety is individual; consult a clinician about your own risk profile.
FDA-Approved Indications
Levothyroxine is FDA-approved for use in the condition categories below. The FDA-approved label’s Indications and Usage section is shown verbatim.
Hypothyroidism Levothyroxine sodium tablets are indicated in adult and pediatric patients, including neonates, as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. Pituitary Thyrotropin (Thyroid‑Stimulating Hormone, TSH) Suppression Levothyroxine sodium tablets are indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.Show full Indications and Usage
Limitations of Use Levothyroxine sodium tablets are not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients as there are no clinical benefits and overtreatment with levothyroxine sodium may induce hyperthyroidism [see Warnings and Precautions (5.1) ]. Levothyroxine sodium tablets are not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis. Levothyroxine sodium tablets are a L-thyroxine (T4) indicated in adult and pediatric patients, including neonates, for: Hypothyroidism: As replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. (1) Pituitary Thyrotropin (Thyroid‑Stimulating Hormone, TSH) Suppression: As an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer. (1) Limitations of Use: Not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients Not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis
Frequently Asked Questions
What are the most-reported side effects of levothyroxine?
Is levothyroxine the same as Synthroid?
Has levothyroxine been recalled?
Is there a current shortage of levothyroxine?
Does levothyroxine have an FDA boxed warning?
Data Sources & Methodology
How each section of this page is sourced, and how often the data is refreshed.
| Source | Endpoint | Refresh |
|---|---|---|
| FAERS reactions | openFDA /drug/event.json count API. Aggregated per drug per reaction term; we do not store individual reports. | Daily |
| Recalls | openFDA /drug/enforcement.json. Drugs matched via three confidence-tracked strategies: structured generic name (HIGH), NDC code bridge (MEDIUM), text token parse (LOW). Only HIGH and MEDIUM matches surface here. | 6 hours |
| Shortages | FDA Drug Shortages list. | Daily |
| Boxed warnings & label sections | openFDA /drug/label.json. Labels are stable; monthly cadence is sufficient. | Monthly |
| Condition categories | Synonym-mapped from drug_labels.indications. Methodology at /methodology/. | Per-drug |
What we do not do. We do not invent, paraphrase, or extrapolate drug claims. Every figure on this page comes from a query against an openFDA endpoint. If the data is unavailable, the section gracefully omits rather than filling the space with editorial guesswork.