Natalizumab adverse event reports that FDA received

Name: Reaction terms in FDA adverse event reports that name Natalizumab
Creator: Reported Reactions
License: https://creativecommons.org/publicdomain/zero/1.0/

Name type: Generic name
Class: Integrin receptor antagonist

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 2 Oct 2026. The data have the reports that FDA received through 30 Jun 2026.

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 2 Oct 2026.

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 2 Oct 2026.

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

Drug reports received through 30 Jun 2026. Device reports have a separate cutoff, 30 Sep 2026. Why a report count is not a rate.

Reports on file

From December 2004 to June 2026, FDA received 2,505 adverse event reports that name Natalizumab. In these reports the drug is a suspect or interacting product.

In the same period, 368 further reports name it only as a concomitant medicine. The counts on this page do not include these reports.

FDA received 65 reports in the 12 months to June 2026 and 134 in the 12 months before. FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.

Of the 1,332,454 drug reports that FDA received in the 12 months to June 2026, 65 (under 0.1%) name Natalizumab. Reports from consumers or other non-health professionals were 8.2% of the reports that name Natalizumab and 45.8% of all drug reports.

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 11 Mar 2026. The site read the page on 2 Oct 2026.

Suspect product

FDA records each drug in a report as suspect, concomitant or interacting. This page counts the reports in which Natalizumab 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 2 Oct 2026.

Data version

openFDA FAERS release of 29 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 2 Oct 2026.

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 11 Mar 2026. The site read the page on 2 Oct 2026.

The latest update of the FDA data, recorded on 28 Oct 2026, changed no count of this page.

In April to June 2026, FDA received 11 reports that name Natalizumab.
In January to March 2026, FDA received 17.
In April to June 2025, FDA received 20.

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.

All updates Feed of updates (RSS)

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 269 reaction terms that 5 or more reports record. A term with fewer than 5 reports is not in the table.

The site keeps reaction terms for 2,493 of the 2,505 reports (99.5%).

The reports of the other years are not in the counts.

So a count in the table can be lower than the count of FDA.

Find a reaction term

The table shows the first 50 of 269 terms.

Reaction terms in the reports that name Natalizumab, most reports first
Reaction term (MedDRA) and plain meaning	Reports	Share of the 2,505 reports
Fatiguetiredness	342	13.7%
Headachehead pain	318	12.7%
Influenza like illnessflu-like symptoms	136	5.4%
Multiple sclerosis	135	5.4%
Multiple sclerosis relapsea flare of multiple sclerosis	131	5.2%
Astheniaweakness or lack of energy	120	4.8%
Nauseafeeling sick	111	4.4%
Dizzinesslight-headedness or unsteadiness	106	4.2%
Urinary tract infectionbladder or urinary infection	100	4%
Painpain, site not specified	98	3.9%
Falla fall	93	3.7%
Depressionlow mood	92	3.7%
Pyrexiafever	81	3.2%
Condition aggravatedthe condition being treated got worse	76	3%
Progressive multifocal leukoencephalopathyPML, a rare brain infection	68	2.7%
Dyspnoeashortness of breath	64	2.6%
Pain in extremitypain in an arm or leg	64	2.6%
Hypoaesthesianumbness	62	2.5%
Balance disorderproblems with balance	61	2.4%
Mobility decreasedreduced ability to move about	60	2.4%
Drug ineffectivethe medicine did not work as expected	56	2.2%
Arthralgiajoint pain	54	2.2%
Feeling abnormalfeeling odd or not right	51	2%
Chillschills or shivering	50	2%
Anxiety	49	2%
Infusion related reactiona reaction during or soon after an infusion	49	2%
Urticariahives	48	1.9%
Gait disturbancedifficulty walking	46	1.8%
Pruritusitching	46	1.8%
Back pain	45	1.8%
Convulsion	45	1.8%
Muscular weaknessmuscle weakness	45	1.8%
Paraesthesiatingling or pins and needles	45	1.8%
Pneumonialung infection	44	1.8%
Rashskin rash	43	1.7%
Nasopharyngitisa cold	41	1.6%
Vomitingbeing sick	41	1.6%
Off label useused for a purpose or in a way not on the label	40	1.6%
Cognitive disorderproblems with thinking or memory	39	1.6%
Diarrhoealoose or frequent stools	39	1.6%
Muscle spasmsmuscle cramps	39	1.6%
Memory impairmentmemory problems	38	1.5%
Chest pain	37	1.5%
Confusional stateconfusion	37	1.5%
Hypersensitivityan allergic-type reaction	37	1.5%
Insomniadifficulty sleeping	37	1.5%
Abdominal painstomach or belly pain	35	1.4%
Tremorshaking	32	1.3%
Covid-19COVID-19 infection	31	1.2%
Malaisegeneral feeling of being unwell	31	1.2%

Download all 269 terms of Natalizumab (CSV)

The counts add to more than 2,505 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 2 Oct 2026.

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.

Same ingredient, other names

Reporters write a brand name or a generic name. Each name has its own page and its own count.

Names of Natalizumab with a page, in the order generic names, brand names, names as reported
Name	Name type	Reports
Natalizumab (this page)	Generic name	2,505
Tysabri	Brand name	173,350

Sum of the separately reported names: 175,855. A report that names two of these names is in the sum two times. The sum is not the number of reports for the ingredient.

FDA says:

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. The site read the page on 2 Oct 2026.

Importantly, the AEMS data by themselves are not an indicator of the safety profile of the drug or biologic.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of 11 Mar 2026. The site read the page on 2 Oct 2026.

Outcomes by year

The table gives the outcomes that the reporters gave, in the terms of FDA.

Outcomes in the reports that name Natalizumab, 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	48	2	0	0	1	0	0	1	46
2005	1,309	132	14	2	92	1	0	39	1,177
2006	57	56	5	0	42	0	0	16	1
2007	517	503	30	4	362	1	0	150	14
2008	12	11	0	1	6	0	0	6	1
2009	12	10	1	0	7	2	0	6	2
2010	5	4	0	1	2	0	0	2	1
2011	15	12	2	1	6	0	0	9	3
2012	23	21	2	2	8	0	0	14	2
2013	22	21	10	1	8	0	0	8	1
2014	26	26	7	0	19	0	0	12	0
2015	14	14	1	1	10	2	0	9	0
2016	12	10	2	1	0	0	1	7	2
2017	7	7	0	0	3	1	1	5	0
2018	14	14	1	1	1	1	0	12	0
2019	22	19	3	1	6	0	0	16	3
2020	30	29	0	5	15	0	2	20	1
2021	41	35	9	4	19	0	0	21	6
2022	40	35	3	6	14	1	0	23	5
2023	43	38	0	5	25	4	6	24	5
2024	132	124	2	3	19	27	0	112	8
2025	69	68	2	3	14	1	1	63	1
2026	35	30	1	1	14	0	2	19	5

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 2 Oct 2026.

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 2 Oct 2026.

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

Reports that name Natalizumab, by the year in which FDA received them

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

Reports that name Natalizumab, by the year in which FDA received them
Year	Reports
2004	1
2005	1,357
2006	44
2007	528
2008	15
2009	13
2010	6
2011	20
2012	24
2013	27
2014	17
2015	10
2016	11
2017	13
2018	17
2019	27
2020	28
2021	43
2022	41
2023	42
2024	125
2025	68
2026	28

Reports that name Natalizumab, by month, five years to June 2026

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 of the patient in the reports that name Natalizumab
Age	Reports	Share
Under 2	11	0.4%
2 to 11	1	under 0.1%
12 to 17	7	0.3%
18 to 44	864	34.5%
45 to 64	1,018	40.6%
65 to 74	66	2.6%
75 and over	9	0.4%
Age not given	529	21.1%

Sex of the patient in the reports that name Natalizumab
Sex	Reports	Share
Female	1,811	72.3%
Male	519	20.7%
Unknown or not given	175	7%

Type of reporter in the reports that name Natalizumab
Reporter	Reports	Share
Physician	417	16.6%
Pharmacist	118	4.7%
Other health professional	530	21.2%
Lawyer	0	0%
Consumer or non-health professional	205	8.2%
Not given	1,235	49.3%

Age and sex are as the report gives them. The reporter is the primary source in the report. 29.4% of the reports give the United States as the country.

Reason for use

Reason for use (indication) that the reports of Natalizumab record
Indication as recorded (MedDRA)	Reports	Share
Multiple sclerosis	2,130	85%
Relapsing-remitting multiple sclerosis	80	3.2%
Relapsing multiple sclerosis	23	0.9%
Crohn's disease	19	0.8%
Crohn's disease	13	0.5%
Concentric sclerosis	5	0.2%

The reporter fills in the indication, and the field is often empty. Each share is of all 2,505 reports.

Pages near this one

Tysabri same ingredient
Entyvio same class
Tyruko same class
Vedolizumab same class
Nasonex next in the A to Z list
Natazia next in the A to Z list
Nasacort Aq next in the A to Z list
Nateglinide next in the A to Z list
Nasacort Allergy 24HR next in the A to Z list
Natpara next in the A to Z list
Nasacort next in the A to Z list
Natulan next in the A to Z list

These links are for navigation. No count selected them. The class page lists each drug of the class.

Official pages

DailyMed labels for NatalizumabThe 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 2 Oct 2026. The links open in a new tab.

Cite this page

Reported Reactions. Natalizumab: adverse event reports that FDA received. https://reportedreactions.com/drug/natalizumab/ Source: U.S. Food and Drug Administration, openFDA Drug Adverse Event (FAERS) files, release of 29 Oct 2026. Reports received through 30 Jun 2026.

Where the data come from

The counts come from the openFDA Drug Adverse Event (FAERS) bulk files, release of 29 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 Nov 2026. A class is the pharmacologic class (EPC) of the FDA label.

A report is in the count when it names Natalizumab as a suspect or interacting product. The 368 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 Natalizumab 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 11 Mar 2026. The site read the page on 2 Oct 2026.

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 Natalizumab?

No. It is a count of what people reported to FDA: 2,505 reports from December 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?

Other health professional (21.2%), physician (16.6%) and consumer or non-health professional (8.2%). 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 2 Oct 2026.

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.

To the top of the page