Synthroidlevothyroxine
276,239 adverse event reports submitted to the FDA (1997–2026)
Top Reported Adverse Events
The most frequently reported events in association with Synthroid in the FAERS database. These are events reported by patients taking this medication, not necessarily caused by it. A single report may include multiple events.
Show these terms with plain-language definitions
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Fatigue 23,406 reports
Extreme tiredness or lack of energy that does not improve with rest.
Full definition in the glossary → See all drugs reporting this event →Nausea 20,081 reports
The feeling of sickness in your stomach that often comes before vomiting.
Full definition in the glossary → See all drugs reporting this event →Drug Ineffective 18,903 reports
A report that the medication did not work as expected for the person taking it. This is a reporting category, not a sign the drug is defective. It simply means someone felt it was not helping their condition.
Full definition in the glossary →Headache 17,068 reports
Pain in the head or upper neck.
Full definition in the glossary → See all drugs reporting this event →Diarrhoea 16,755 reports
Loose or watery bowel movements, often frequent. Also spelled diarrhea in American English.
Full definition in the glossary → See all drugs reporting this event →Dyspnoea 14,954 reports
Shortness of breath or difficulty breathing. Also spelled dyspnea in American English.
Full definition in the glossary → See all drugs reporting this event →Pain 14,888 reports
A general report of physical discomfort, used when no more specific location is given.
Full definition in the glossary →Dizziness 13,782 reports
A feeling of being lightheaded, unsteady, or like the room is spinning.
Full definition in the glossary → See all drugs reporting this event →Off Label Use 12,335 reports
Using a medication for a condition or in a way that the FDA has not officially approved. This is common and often legal, and a report of it does not mean something went wrong. Doctors sometimes prescribe drugs off label based on their judgment.
Full definition in the glossary →Arthralgia 11,976 reports
Asthenia 11,785 reports
Physical weakness or lack of strength.
Full definition in the glossary →Malaise 10,987 reports
A general feeling of being unwell or uncomfortable, without a specific symptom.
Full definition in the glossary →Fall 10,736 reports
A report that the person fell down. Falls are tracked because they can signal issues like dizziness, weakness, or balance problems.
Full definition in the glossary →Vomiting 10,704 reports
Throwing up the contents of the stomach.
Full definition in the glossary → See all drugs reporting this event →Weight Decreased 8,921 reports
Ranked by frequency of reports, not severity. The most-reported event is not necessarily the most dangerous or the most common in patients taking this drug.
Who Is Reporting
Demographics of patients in FAERS reports that included this information. Not all reports include patient demographics.
By Sex
View reporter sex data as a table
| Sex | Reports |
|---|---|
| Female | 209,292 |
| Male | 50,449 |
| Unknown | 357 |
By Age Group
View age group data as a table
| Age group | Reports |
|---|---|
| 0-17 | 2,707 |
| 18-34 | 7,176 |
| 35-49 | 22,361 |
| 50-64 | 53,154 |
| 65-74 | 43,483 |
| 75+ | 42,164 |
This shows who filed reports, reflecting who takes this drug and who tends to report, not who is at greatest risk.
Reported Outcomes
Outcomes recorded in FAERS reports that included Synthroid. A single report may involve multiple reactions, each with a different outcome. These categories are defined by FDA reporting guidelines, not by PillSignal.
View outcome data as a table
| Outcome | Reports |
|---|---|
| Non-Serious | 110,410 |
| Other Serious | 105,967 |
| Hospitalization | 80,338 |
| Death | 18,181 |
| Life-Threatening | 9,427 |
| Disability | 8,244 |
Serious outcomes are far more likely to be reported than mild ones, so this overstates how often outcomes are serious. A recorded death does not mean the drug caused it.
Report Volume Over Time
Number of FAERS reports received per quarter for Synthroid. Changes in volume may reflect shifts in prescribing rates, media attention, or reporting behavior, not changes in the medication's safety profile.
View report trend as a table
| Year | Reports |
|---|---|
| 1997 | 1 |
| 1998 | 2 |
| 2000 | 1 |
| 2001 | 1 |
| 2002 | 2 |
| 2003 | 1 |
| 2004 | 5,678 |
| 2005 | 6,022 |
| 2006 | 6,274 |
| 2007 | 6,353 |
| 2008 | 8,198 |
| 2009 | 8,929 |
| 2010 | 11,697 |
| 2011 | 12,718 |
| 2012 | 15,041 |
| 2013 | 9,851 |
| 2014 | 11,102 |
| 2015 | 16,315 |
| 2016 | 16,835 |
| 2017 | 15,456 |
| 2018 | 15,037 |
| 2019 | 14,922 |
| 2020 | 17,217 |
| 2021 | 15,388 |
| 2022 | 16,279 |
| 2023 | 14,415 |
| 2024 | 14,131 |
| 2025 | 14,853 |
| 2026 (partial) | 3,520 |
The steep increase around 2004 reflects the FDA's move to electronic submission, not a change in this drug's safety. Trends track reporting volume, not risk.
Medications commonly reported with Synthroid
In FDA adverse event reports that mention Synthroid, these medications appeared most often in the same report.
- Ergocalciferol (38,214 reports)
- Aspirin (36,638 reports)
- Furosemide (29,682 reports)
- Omeprazole (28,259 reports)
- Acetaminophen (25,447 reports)
This reflects co-occurrence in submitted reports, not evidence of drug interaction or combined risk. People often report several medications taken for the same condition or for unrelated reasons. Talk to a doctor or pharmacist about your specific medications.
Related Drugs
Other medications with similar adverse event profiles in FDA FAERS reports.
Data Source
This data is sourced from the FDA's Adverse Event Monitoring System (AEMS), formerly FAERS, via the OpenFDA API. PillSignal is not affiliated with the FDA.
View this data on the FDA website →Data last updated: June 2026