Chlorzoxazone adverse event reports that FDA received
- Name type
- Generic name
- Class
- Muscle relaxant
What a report is
A report is not proof that the drug was the cause of the event.
FDA says:
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.
Source: openFDA, Drug Adverse Event Overview, section "Responsible use of the data". The site read the page on . The data have the reports that FDA received through .
FDA also says:
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 has not been scientifically or otherwise verified as to a cause and effect relationship and cannot be used to estimate the incidence of these events.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
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.
Source: openFDA, Response of the drug event API (meta.disclaimer). The site read the page on .
Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.
Reports on file
From May 2004 to June 2026, FDA received 328 adverse event reports that name Chlorzoxazone. In these reports the drug is a suspect or interacting product.
In the same period, 963 further reports name it only as a concomitant medicine. The counts on this page do not include these reports.
FDA received 15 reports in the 12 months to June 2026 and 6 in the 12 months before. FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.
The number of people who use the product is not in the data. A count is not a rate. A count of reports is not a count of events or of patients, because one event can have more than one report.
There are many instances of duplicative reports and some reports do not contain all the necessary information.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
Suspect product
FDA records each drug in a report as suspect, concomitant or interacting. This page counts the reports in which Chlorzoxazone is suspect or interacting. FDA says:
Any number of the drugs may be marked as suspect if thought to be responsible for one or more of the reactions, but that information is not validated.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
Data version
openFDA FAERS release of 1 Oct 2026. Reports received through 30 Jun 2026.
Since the last update
FDA says:
Many factors can influence whether or not an event will be reported, such as the time a product has been marketed and publicity about an event.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
The information in these reports cannot be used to estimate the incidence (occurrence rates) of the events reported.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
No update is on record for this page. The record starts when FDA adds the reports of July to September 2026.
- In April to June 2026, FDA received 9 reports that name Chlorzoxazone.
- In January to March 2026, FDA received 4.
- In April to June 2025, FDA received 2.
April to June 2026 is the latest closed quarter in the data. A closed quarter is a quarter for which the FDA files have most of the reports.
Reaction lookup
These are the reaction terms that the reports record, with the number of reports for each term. Type a term or a plain word to find its count.
What this list leaves out
The table lists the 27 reaction terms that 5 or more reports record. A term with fewer than 5 reports is not in the table.
This list is partial.
It covers 222 of the 328 reports (67.7%).
The site keeps reaction terms only for years in which the drug has 12 or more reports.
So a count in the table can be lower than the count of FDA.
The table shows all 27 terms.
| Reaction term (MedDRA) and plain meaning | Reports | Share of the 328 reports |
|---|---|---|
| Dizzinesslight-headedness or unsteadiness | 35 | 10.7% |
| Drug ineffectivethe medicine did not work as expected | 26 | 7.9% |
| Somnolencedrowsiness | 23 | 7% |
| Nauseafeeling sick | 20 | 6.1% |
| Completed suicidedeath by suicide | 18 | 5.5% |
| Toxicity to various agentspoisoning or toxic effect of one or more substances | 16 | 4.9% |
| Headachehead pain | 15 | 4.6% |
| Drug hypersensitivityan allergic-type reaction (the term names a medicine) | 14 | 4.3% |
| Stevens-Johnson syndromea severe skin and mucous-membrane reaction | 14 | 4.3% |
| Secondary adrenocortical insufficiency | 11 | 3.4% |
| Diarrhoealoose or frequent stools | 10 | 3% |
| Muscle spasmsmuscle cramps | 10 | 3% |
| Coma | 9 | 2.7% |
| Fatiguetiredness | 8 | 2.4% |
| Gait disturbancedifficulty walking | 7 | 2.1% |
| Weight decreasedweight loss | 7 | 2.1% |
| Cardio-respiratory arrestthe heart and breathing stopped | 6 | 1.8% |
| Hepatic cytolysis | 6 | 1.8% |
| Peptic ulcer | 6 | 1.8% |
| Pruritusitching | 6 | 1.8% |
| Renal failurekidney failure | 6 | 1.8% |
| Renal impairmentreduced kidney function | 6 | 1.8% |
| Sensory disturbancea change in sensation | 6 | 1.8% |
| Suicide attempta suicide attempt | 6 | 1.8% |
| Depressed level of consciousness | 5 | 1.5% |
| Spinal column injury | 5 | 1.5% |
| Vomitingbeing sick | 5 | 1.5% |
The counts add to more than 328 reports, because one report can record more than one term. FDA says:
No individual drug is connected to any individual reaction. When a report lists multiple drugs and multiple reactions, there is no way to conclude from the data therein that a given drug is responsible for a given reaction.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
The CSV file has the same rows and the same limits. Its last row is a note that says so.
MedDRA term
The person who codes a report selects the preferred term that agrees best with the description of the reporter. The words under a term are the plain meaning that this site gives.
Not the label
The FDA-approved label of a product lists its adverse reactions. See the official pages at the end of this page.
Outcomes by year
The table gives the outcomes that the reporters gave, in the terms of FDA.
Outcomes in the reports that name Chlorzoxazone, by the year of the openFDA file that holds the report
The table continues to the right.
| Year of the openFDA file | Reports | Serious | Death | Life-threatening | Hospitalization (initial or prolonged) | Disability or Permanent Damage | Congenital Anomaly/Birth Defect | Other Serious (Important Medical Events) | Not serious |
|---|---|---|---|---|---|---|---|---|---|
| 2004 | 10 | 10 | 7 | 0 | 1 | 0 | 0 | 3 | 0 |
| 2005 | 6 | 6 | 3 | 0 | 4 | 0 | 0 | 3 | 0 |
| 2006 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2007 | 8 | 7 | 1 | 2 | 3 | 0 | 0 | 4 | 1 |
| 2008 | 3 | 2 | 0 | 0 | 1 | 0 | 0 | 1 | 1 |
| 2009 | 5 | 5 | 0 | 3 | 1 | 0 | 0 | 4 | 0 |
| 2010 | 3 | 2 | 0 | 0 | 1 | 0 | 0 | 2 | 1 |
| 2011 | 11 | 11 | 7 | 2 | 1 | 0 | 0 | 2 | 0 |
| 2012 | 11 | 11 | 6 | 1 | 2 | 0 | 0 | 3 | 0 |
| 2013 | 3 | 3 | 2 | 0 | 1 | 0 | 0 | 1 | 0 |
| 2014 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2015 | 11 | 6 | 5 | 1 | 2 | 1 | 0 | 1 | 5 |
| 2016 | 45 | 15 | 9 | 0 | 5 | 0 | 0 | 3 | 30 |
| 2017 | 42 | 6 | 1 | 0 | 5 | 0 | 0 | 2 | 36 |
| 2018 | 47 | 17 | 7 | 1 | 2 | 0 | 0 | 14 | 30 |
| 2019 | 56 | 26 | 10 | 1 | 10 | 1 | 0 | 15 | 30 |
| 2020 | 19 | 16 | 12 | 1 | 3 | 1 | 0 | 14 | 3 |
| 2021 | 3 | 3 | 1 | 0 | 0 | 0 | 0 | 3 | 0 |
| 2022 | 6 | 4 | 0 | 0 | 1 | 0 | 0 | 4 | 2 |
| 2023 | 10 | 7 | 0 | 0 | 5 | 1 | 0 | 5 | 3 |
| 2024 | 7 | 7 | 3 | 0 | 1 | 1 | 0 | 6 | 0 |
| 2025 | 9 | 9 | 1 | 1 | 6 | 0 | 0 | 6 | 0 |
| 2026 | 13 | 12 | 0 | 1 | 9 | 1 | 1 | 10 | 1 |
An outcome in a report is not proof that the drug was the cause. The reporter gives the outcome, and FDA does not verify it. FDA says:
The information in these reports has not been scientifically or otherwise verified as to a cause and effect relationship and cannot be used to estimate the incidence of these events.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
The six headings with the names of FDA are the outcome terms of FDA. A report can have more than one outcome. The columns Serious and Not serious are the two values of the openFDA field serious. For the value serious, openFDA gives this description:
The adverse event resulted in death, a life threatening condition, hospitalization, disability, congenital anomaly, or other serious condition
Source: openFDA, Drug adverse event fields (YAML reference). The site read the page on .
The year is the year of the openFDA file that holds the latest version of the report. It is not always the year in which FDA first received the report. The chart of the next section uses the year of first receipt. The latest year is not complete.
Reports by year and month
The column of 2026 has an outline, because the year is not complete. It has the reports that FDA received through June 2026 only.
Show the figures of the chart as a table
| Year | Reports |
|---|---|
| 2004 | 10 |
| 2005 | 6 |
| 2007 | 8 |
| 2008 | 3 |
| 2009 | 5 |
| 2010 | 2 |
| 2011 | 8 |
| 2012 | 16 |
| 2013 | 4 |
| 2014 | 2 |
| 2015 | 10 |
| 2016 | 48 |
| 2017 | 45 |
| 2018 | 44 |
| 2019 | 58 |
| 2020 | 13 |
| 2021 | 6 |
| 2022 | 6 |
| 2023 | 10 |
| 2024 | 7 |
| 2025 | 4 |
| 2026 | 13 |
FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.
Why a count moves
A count moves for many reasons. The guide gives FDA's words about them.
Patients and reporters
| Age | Reports | Share | Share as a bar |
|---|---|---|---|
| Under 2 | 0 | 0% | |
| 2 to 11 | 0 | 0% | |
| 12 to 17 | 0 | 0% | |
| 18 to 44 | 64 | 19.5% | |
| 45 to 64 | 95 | 29% | |
| 65 to 74 | 39 | 11.9% | |
| 75 and over | 22 | 6.7% | |
| Age not given | 108 | 32.9% |
| Sex | Reports | Share | Share as a bar |
|---|---|---|---|
| Female | 207 | 63.1% | |
| Male | 87 | 26.5% | |
| Unknown or not given | 34 | 10.4% |
| Reporter | Reports | Share | Share as a bar |
|---|---|---|---|
| Physician | 69 | 21% | |
| Pharmacist | 51 | 15.5% | |
| Other health professional | 74 | 22.6% | |
| Lawyer | 1 | 0.3% | |
| Consumer or non-health professional | 122 | 37.2% | |
| Not given | 11 | 3.4% |
Age and sex are as the report gives them. The reporter is the primary source in the report. 72.3% of the reports give the United States as the country.
Reason for use
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Muscle spasms | 13 | 4% |
| Back pain | 7 | 2.1% |
| Neck pain | 5 | 1.5% |
| Pain | 5 | 1.5% |
| Muscle relaxant therapy | 3 | 0.9% |
| Musculoskeletal pain | 2 | 0.6% |
The reporter fills in the indication, and the field is often empty. Each share is of all 328 reports.
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These links are for navigation. No count selected them. The class page lists each drug of the class.
Official pages
- DailyMed labels for ChlorzoxazoneThe labels (prescribing information) that have this name, at the National Library of Medicine.
- MedWatch Online Voluntary Reporting FormThe online form of FDA for a voluntary report.
- MedWatch: The FDA Safety Information and Adverse Event Reporting ProgramThe page of the FDA program that receives reports about drugs and devices.
- FDA Adverse Event Monitoring System (AEMS) Public DashboardThe public dashboard of FDA for adverse event reports on drugs and biologics.
The site checked these addresses on . The links open in a new tab.
Cite this page
Reported Reactions. Chlorzoxazone: adverse event reports that FDA received. https://reportedreactions.com/drug/chlorzoxazone/ Source: U.S. Food and Drug Administration, openFDA Drug Adverse Event (FAERS) files, release of . Reports received through .
Where the data come from
The counts come from the openFDA Drug Adverse Event (FAERS) bulk files, release of 1 Oct 2026. The files have the reports that FDA received through 30 Jun 2026. A drug name is the name on the report. The site matches it to a brand name or a generic name of the National Drug Code Directory of 2 Oct 2026. A class is the pharmacologic class (EPC) of the FDA label.
A report is in the count when it names Chlorzoxazone as a suspect or interacting product. The 963 reports that name it only as a concomitant medicine are not in the count. The site does not publish a report narrative, a lot number, a detail of a patient or the identity of a reporter. The record of FDA is the authority. See how the site counts reports, the data sources and the corrections page.
Questions
Do these reports show that Chlorzoxazone was responsible for the reactions?
No. FDA says:
For any given report, there is no certainty that a suspected drug caused the event.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
A reaction can relate to the condition that the drug treats, to other medicines, or to something else.
Is this the list of reactions on the label of Chlorzoxazone?
No. It is a count of what people reported to FDA: 328 reports from May 2004 to June 2026. The FDA-approved label of a product lists its adverse reactions. The official pages at the end of this page link to the labels.
Who sent these reports?
Consumer or non-health professional (37.2%), other health professional (22.6%) and physician (21%). These are the types of reporter for the reports that name this drug.
If a manufacturer receives an adverse event report, it is normally required to send the report to FDA.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
How does a person report an adverse event?
FDA runs MedWatch, a program that takes voluntary reports from health professionals, patients and consumers. The guide on how to report has the links.