· Brand: Synthroid, Euthyrox + 9 more

Levothyroxine Side Effects: Common, Serious & FDA Warnings

Creator: MedivaScan
Published: 2026-05-28T04:28:23.512865+00:00

Verified from FDA on June 23, 2026Refreshes every 6 hoursFDA-Sourced

FDA-Approved For

Quick answer

Based on 308,000+ FDA adverse event reports, the most-reported levothyroxine reactions include fatigue, nausea, and headache. FDA reports 38 active Class II recalls of levothyroxine, primarily for failed dissolution specifications. The FDA-approved label carries a boxed warning.

For information only. MedivaScan summarizes public FDA data and is not medical advice. Consult a healthcare professional before changing any medication. If you experience a serious reaction, contact your doctor or call 911.

FDA 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	26,244	8.5%
Nausea	22,333	7.2%
Headache	19,112	6.2%
Diarrhoea	18,461	6.0%
Dyspnoea	16,479	5.3%
Pain	16,162	5.2%
Dizziness	15,622	5.1%
Arthralgia	13,171	4.3%
Asthenia	13,356	4.3%
Malaise	12,289	4.0%

Source: FDA FAERS·Updated June 23, 2026·n=308,725+·verify on FDA →·Methodology

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
Serious reports (any flag)	185,740
Hospitalization	89,563

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) ].
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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) ] .

Source: DailyMed (levothyroxine label)·Updated June 23, 2026

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 →); closed recalls are grouped in the disclosure that follows.

Date	Reason	Class	Quantity	Status
2026-07-08	Subpotent Drug ACCORD HEALTHCARE, INC.	Class II	6432 bottles	Ongoing
2026-04-01	Subpotent Drug MACLEODS PHARMA USA, INC	Class II	1315 bottles	Ongoing
2026-01-21	Product Mix-Up: A single bottle of this lot was reported by a pharmacy to contain 88 mcg tablets instead of 150 mcg tablets. Alvogen, Inc	Class II	—	Ongoing
2025-10-15	Subpotent: During long term stability testing of Levothyroxine Sodium Tablets USP for 88 mcg, the assay content was observed below the approved specification range. ACCORD HEALTHCARE, INC.	Class II	54,432 bottles	Ongoing
2025-08-20	Subpotent drug Pfizer	Class II	29, 004 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	54,227 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	2,344 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	82,159 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	4,921 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	4,896 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	2,352 bottles	Ongoing
2025-07-23	Subpotent Drug: Assay below the approved specification ACCORD HEALTHCARE, INC.	Class II	9,739 bottles	Ongoing
2025-06-18	Presence of a foreign substance: black hair found embedded in tablet. Macleods Pharmaceuticals Ltd	Class III	1,344- 1000 count bottles	Ongoing
2025-05-07	Subpotent ACCORD HEALTHCARE, INC.	Class II	4,888 Bottles	Ongoing
2025-05-07	Subpotent ACCORD HEALTHCARE, INC.	Class II	4,872 Bottles	Ongoing
2025-05-07	Subpotent ACCORD HEALTHCARE, INC.	Class II	4,885 Bottles	Ongoing
2025-05-07	Subpotent ACCORD HEALTHCARE, INC.	Class II	18,984 Bottles	Ongoing
2025-03-26	Super-Potent Drug: Out of specification potency results were obtained. Mylan Institutional, Inc.	Class II	1,068 cartons	Ongoing
2025-03-26	Super-Potent Drug: Out of specification potency results were obtained. Mylan Institutional, Inc.	Class II	347 Cartons	Ongoing

Source: FDA Drug Enforcement Reports·Updated June 23, 2026·Refreshes every 6 hours·verify on FDA →

Show 1 closed recall (2025 to 2025)

Includes resolved and terminated recalls matched to levothyroxine. Most recent first.

Date	Reason	Class	Quantity	Status
2025-01-08	Failed Impurities/Degradation Specifications: Out of specifications result observed in the drug substance for impurity test during 3-month long term stability study. Lupin Pharmaceuticals Inc.	Class II	480 1000-count bottles	Terminated

Levothyroxine Shortages

FDA-listed shortages of levothyroxine products. Strength and dosage-form level detail.

No active or recent shortages of levothyroxine are listed. We refresh this view daily.

Source: FDA Drug Shortages·Updated June 23, 2026

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.

Source: DailyMed (levothyroxine label)·Updated June 23, 2026

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.
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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

Source: DailyMed (levothyroxine label)·Updated June 23, 2026·Section 1 (Indications and Usage)

Frequently Asked Questions

What are the most-reported side effects of levothyroxine?

Fatigue, nausea, and headache are among the most-reported reactions in FDA FAERS data for levothyroxine. The full ranking, with reaction counts and the share of total reports, is in the Common Side Effects table above. Reports indicate co-occurrence, not causation; consult a clinician about your specific case.

Is levothyroxine the same as Synthroid?

Levothyroxine is the generic name; Synthroid is a brand name for the same active ingredient. Other brand names include Euthyrox, Levo-T, Tirosint Sol, Tirosint-Sol, Ermeza, Unithroid, Levoxyl, Thyquidity, Thyro-Tabs, and Tirosint. The active ingredient is identical; formulation and inactive ingredients may vary by manufacturer.

Has levothyroxine been recalled?

Yes. Levothyroxine has active and closed recalls on record in the FDA enforcement database. Reasons are dominated by subpotent or out-of-spec content and contamination or foreign material. See the recalls table on this page for current counts, firm names, dates, and lot quantities.

What are levothyroxine's current ongoing recalls about?

Active levothyroxine recalls are listed in the recalls table above with their class, reason, firm, and affected lots. The dominant reasons across these recalls are subpotent or out-of-spec content and contamination or foreign material. For lot numbers, distribution patterns, and the FDA enforcement record for any individual recall, follow the verify-on-FDA link from each row.

What do FDA recall classes mean?

Class I means a reasonable probability of serious adverse health consequences or death. Class II means temporary or medically reversible adverse health consequences with remote probability of serious harm. Class III means use of the product is unlikely to cause adverse health consequences. The class assignment is the FDA's, not the manufacturer's.

Does levothyroxine have an FDA boxed warning?

Yes. The FDA-approved label for levothyroxine carries a boxed warning. Boxed warnings are the FDA's strongest cautions. See the "FDA Boxed Warning" section above for the verbatim warning text.

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.