Leflunomide
According to the FDA label: Leflunomide tablets are indicated for the treatment of adults with active rheumatoid arthritis (RA). Leflunomide is a pyrimidine synthesis inhibitor indicated for the treatment of adults with active rheumatoid arthritis. ( 1 )
63,576 adverse event reports submitted to the FDA (2004–2026)
Top Reported Adverse Events
The most frequently reported events in association with Leflunomide 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.
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Drug Ineffective 23,052 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 →Rheumatoid Arthritis 15,930 reports
An autoimmune condition where the immune system attacks the joints, causing pain and swelling. It often appears in reports because it is a condition being treated, not always a reaction.
Full definition in the glossary →Pain 13,070 reports
A general report of physical discomfort, used when no more specific location is given.
Full definition in the glossary →Arthralgia 11,711 reports
Joint Swelling 11,522 reports
Swelling in or around a joint.
Full definition in the glossary →Drug Intolerance 11,270 reports
A report that the person could not tolerate a medication, often due to uncomfortable effects.
Full definition in the glossary →Fatigue 10,635 reports
Extreme tiredness or lack of energy that does not improve with rest.
Full definition in the glossary → See all drugs reporting this event →Rash 10,058 reports
An area of irritated, red, or bumpy skin.
Full definition in the glossary → See all drugs reporting this event →Off Label Use 9,253 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 →Synovitis 8,400 reports
Inflammation of the lining of a joint, causing swelling and pain.
Full definition in the glossary →Contraindicated Product Administered 7,885 reports
A report that a medication was given in a situation where it was not recommended, for example when another condition made it unsuitable. This is a reporting category describing what happened, not a measure of harm by itself.
Full definition in the glossary →Condition Aggravated 7,717 reports
A report that the person's existing health condition got worse. This describes a worsening of something the person already had, not necessarily a new problem caused by the drug.
Full definition in the glossary →Arthropathy 7,394 reports
Any disease or disorder of a joint.
Full definition in the glossary →Alopecia 7,202 reports
Hypersensitivity 7,146 reports
An exaggerated reaction by the immune system, similar to an allergic reaction.
Full definition in the glossary →
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 | 45,696 |
| Male | 10,732 |
| Unknown | 67 |
By Age Group
View age group data as a table
| Age group | Reports |
|---|---|
| 0-17 | 716 |
| 18-34 | 1,725 |
| 35-49 | 11,416 |
| 50-64 | 15,746 |
| 65-74 | 7,333 |
| 75+ | 3,181 |
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 Leflunomide. 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 |
|---|---|
| Other Serious | 44,918 |
| Hospitalization | 19,253 |
| Non-Serious | 10,037 |
| Disability | 8,705 |
| Death | 7,068 |
| Life-Threatening | 6,815 |
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 Leflunomide. 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 |
|---|---|
| 2004 | 486 |
| 2005 | 444 |
| 2006 | 250 |
| 2007 | 364 |
| 2008 | 631 |
| 2009 | 691 |
| 2010 | 720 |
| 2011 | 657 |
| 2012 | 884 |
| 2013 | 1,231 |
| 2014 | 1,145 |
| 2015 | 1,673 |
| 2016 | 2,764 |
| 2017 | 3,738 |
| 2018 | 4,646 |
| 2019 | 5,997 |
| 2020 | 9,148 |
| 2021 | 6,726 |
| 2022 | 6,179 |
| 2023 | 4,525 |
| 2024 | 5,416 |
| 2025 | 4,581 |
| 2026 (partial) | 680 |
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 Leflunomide
In FDA adverse event reports that mention Leflunomide, these medications appeared most often in the same report.
- Adalimumab (28,014 reports)
- Etanercept (27,003 reports)
- Prednisone (23,534 reports)
- Sulfasalazine (21,078 reports)
- Abatacept (20,568 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