Pharmacologic class (EPC) · 6 drug pages

l-Thyroxine: adverse event reports filed with FDA

51,210 reports list a drug in this class as a suspect or interacting product, 2004–2026.

Read first · FDA's statement on these data

Adverse event reports submitted to FDA do not undergo extensive validation or verification. Therefore, a causal relationship cannot be established between product and reactions listed in a report. While a suspected relationship may exist, it is not medically validated and should not be the sole source of information for clinical decision making or other assumptions about the safety or efficacy of a product. Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product. openFDA, FDA

FDA adds: "There is no certainty that the reported event (adverse event or medication error) was actually due to the product. FDA does not require that a causal relationship between a product and event be proven, and reports do not always contain enough detail to properly evaluate an event." The information in these reports "cannot be used to estimate the incidence of these events."

Do not rely on openFDA to make decisions regarding medical care. While we make every effort to ensure that data is accurate, you should assume all results are unvalidated.

Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.

51,210
reports across the class: 0.3% of all reports; 3,361
reports, 12 months to June 2026: 3,004 in the 12 months before; 48.4%
marked serious by the reporter: 57.4% across all reports; 6
drugs with a page: brand and generic names counted separately

l-Thyroxine is a pharmacologic class (an FDA Established Pharmacologic Class) with 6 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 51,210 adverse event reports received by FDA, 0.3% of the database, from January 2004 to June 2026.

3,361 reports arrived in the 12 months to June 2026, up 12% from 3,004 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 48.4% of the class's reports are marked serious, 6.2% record death among the outcomes and 17.2% record hospitalisation, as reported.

Across the class the reactions recorded most often are fatigue (11.8%), drug ineffective (9.2%) and headache (7.3%). The class median share shown beside each term is the middle value across the member drugs; it is the comparison used on every drug page in this class.

The members table is ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Drugs in the class

Drug	Name type	Reports	Latest 12 months	Marked serious	Top term recorded
SynthroidLevothyroxine sodium	brand	26,831	1,910	38.1%	Fatigue
Levothyroxine sodium	generic	14,372	1,013	66.1%	Fatigue
EuthyroxLevothyroxine sodium	brand	3,596	133	89.6%	Fatigue
LevoxylLevothyroxine sodium	brand	3,382	70	27.7%	Drug ineffective
TirosintLevothyroxine sodium	brand	2,276	205	17%	Fatigue
NP ThyroidThyroid tablets	brand	753	30	66.8%	Fatigue

Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Reports by month, five years

FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

Reactions recorded across the class

share of class reports recording the termmedian drug in the class

Fatiguetiredness11.8%6,023
Drug ineffectivethe medicine did not work as expected9.2%4,692
Headachehead pain7.3%3,730
Alopeciahair loss6.9%3,539
Palpitationsawareness of the heartbeat6%3,057
Malaisegeneral feeling of being unwell6%3,050
Dyspnoeashortness of breath5.7%2,908
Painpain, site not specified5.5%2,825
Feeling abnormalfeeling odd or not right5.5%2,815
Nauseafeeling sick5.4%2,785
Weight increasedweight gain5.4%2,764
Dizzinesslight-headedness or unsteadiness5%2,557
Insomniadifficulty sleeping4.8%2,436
Anxietyanxiety4.7%2,427
Astheniaweakness or lack of energy4.6%2,371
Blood thyroid stimulating hormone increased4.1%2,086
Diarrhoealoose or frequent stools4%2,023
Hypothyroidismunderactive thyroid3.5%1,799
Arthralgiajoint pain3.5%1,777
Falla fall3.3%1,713
Rashskin rash3.3%1,666
Weight decreasedweight loss3.1%1,591
Pruritusitching3.1%1,583
Hypertensionhigh blood pressure3%1,550
Constipationconstipation3%1,534

Solid bar: share of all class reports. Hollow bar: the median share across the 6 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death6.2%3,173

Life-threatening3.1%1,586

Hospitalisation (initial or prolonged)17.2%8,799

Disability2.2%1,149

Congenital anomaly0.6%287

Other serious35.3%18,081

Not serious51.6%26,424

Patient age

Under 20.4%186

2 to 110.4%187

12 to 170.4%226

18 to 447%3,560

45 to 6416.6%8,488

65 to 749.7%4,944

75 and over10.2%5,202

Age not given55.5%28,417

Who reported

Physician10.7%5,469

Pharmacist3.4%1,748

Other health professional12.6%6,465

Lawyer0.7%342

Consumer or non-health professional69%35,335

Not given3.6%1,851

Grey bar: all 20,646,523 reports in the database. Outcome flags are as the reporter set them and are not verified by FDA.

Questions about l-Thyroxine reports

Which drugs are in the l-Thyroxine class on this site?

Synthroid, Levothyroxine sodium, Euthyrox, Levoxyl, Tirosint and NP Thyroid. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

51,210 reports through June 2026, 3,361 of them in the latest 12 months. A report listing two drugs of the class counts once for each.

What reactions are recorded most often?

fatigue (11.8%), drug ineffective (9.2%), headache (7.3%), alopecia (6.9%) and palpitations (6%).

Can the members table be used to rank the drugs?

No. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." Drugs differ in how many people take them, in the conditions they treat, in time on the market and in how diligently reports are collected.

How do I report an adverse event?

Through FDA MedWatch (Form FDA 3500, or 1-800-FDA-1088) or to the manufacturer. See the guide on how to report.

Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A class is the Established Pharmacologic Class most often attached to a drug's reports by openFDA's label harmonisation, or from the NDC Directory where reports carry none. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.

Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.