MedDRA preferred term

Encephalitis: adverse event reports recording this term

6,794 reports to FDA record it, 2004–2026; 0% of the database.

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.

6,794
reports recording the term: 0% of all reports; 465
reports, 12 months to June 2026: 488 in the 12 months before; 99.5%
marked serious by the reporter: 57.4% across all reports; 22.4%
record death among outcomes, as reported: 9.1% across all reports

"Encephalitis" is a MedDRA preferred term recorded in 6,794 adverse event reports received by FDA, 0% of the database, from January 2004 to June 2026. The term is chosen by whoever codes the report to match what the reporter described.

465 reports recorded it in the 12 months to June 2026, close to the 488 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Of reports recording this term, 99.5% are marked serious, 22.4% include death among the outcomes and 65% include hospitalisation, as reported.

The drugs listed most often as suspect products in those reports are Prednisone, Methotrexate and Tacrolimus. That order mostly follows how many reports each drug has overall; the table also gives the term's share within each drug's own reports. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."

Reports by month, five years

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

Drugs listed as suspect products in these reports

Drug	Class	Reports with this term	Share of the drug's own reports
Prednisone	Corticosteroid	418	0.2%
Methotrexate	Folate analog metabolic inhibitor	396	0.2%
Tacrolimus	Calcineurin inhibitor immunosuppressant	279	0.3%
Rituximab	CD20-directed cytolytic antibody	276	0.2%
Cyclophosphamide	Alkylating drug	274	0.2%
Mycophenolate mofetil	Antimetabolite immunosuppressant	263	0.3%
Keytruda	Programmed death Receptor-1 blocking antibody	228	0.4%
Dexamethasone	Corticosteroid	222	0.2%
Prednisolone	Corticosteroid	221	0.3%
Humira	—	201	0%
Nivolumab	Programmed death Receptor-1 blocking antibody	197	0.4%
Opdivo	Programmed death Receptor-1 blocking antibody	188	0.4%
Cytarabine	Nucleoside metabolic inhibitor	159	0.3%
Carboplatin	Platinum-based drug	158	0.2%
Atezolizumab	Programmed death Receptor-1 blocking antibody	152	0.8%
Enbrel	Tumor necrosis factor blocker	146	0%
Pembrolizumab	Programmed death Receptor-1 blocking antibody	141	0.5%
Methylprednisolone	Corticosteroid	135	0.3%
Etoposide	Topoisomerase inhibitor	124	0.2%
Fludarabine	Nucleoside metabolic inhibitor	116	0.6%
Tecentriq	Programmed death Receptor-1 blocking antibody	114	0.7%
Tysabri	Integrin receptor antagonist	107	0.1%
Remicade	Tumor necrosis factor blocker	106	0.1%
Yervoy	CTLA-4-directed blocking antibody	101	0.5%
Vincristine	—	95	0.2%

Drugs with a page on this site, ordered by the number of their reports recording this term. The last column is the term's share within that drug's own reports, against 0% across the whole database. 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."

By pharmacologic class

Class	Reports with this term	Share of class reports	Median drug in class
Corticosteroid	1,092	0.1%	0%
Programmed death Receptor-1 blocking antibody	1,028	0.5%	0.5%
Folate analog metabolic inhibitor	480	0.2%	0.1%
Calcineurin inhibitor immunosuppressant	438	0.2%	0.1%
Alkylating drug	431	0.2%	0.1%
CD20-directed cytolytic antibody	430	0.1%	0.1%
Nucleoside metabolic inhibitor	428	0.1%	0%
Tumor necrosis factor blocker	422	0%	0%
Antimetabolite immunosuppressant	335	0.3%	0.2%
Kinase inhibitor	289	0%	0%

Classes ordered by count. Class shares follow the class's overall report volume as much as anything else.

Patients in these reports

Patient age

Under 21.2%82

2 to 115.3%363

12 to 172.8%193

18 to 4415.9%1,083

45 to 6425.6%1,739

65 to 7413.1%889

75 and over8.5%579

Age not given27.5%1,866

Patient sex

Female45.7%3,102

Male42%2,853

Not given12.3%839

Grey bar: all 20,646,523 reports in the database. 29% of these reports give the United States as the country.

Questions about "Encephalitis"

What does "Encephalitis" mean in an adverse event report?

It is a MedDRA preferred term, the dictionary FDA uses to code what a reporter described. The report's own description is not published by openFDA and is not shown here.

How many reports record encephalitis?

6,794 reports through June 2026 (0% of all reports), 465 of them in the latest 12 months.

Which drugs appear most often in these reports?

Prednisone (418), Methotrexate (396), Tacrolimus (279), Rituximab (276) and Cyclophosphamide (274). Drugs with many reports overall lead almost every term's list. 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."

Does a drug appearing here mean it was responsible for this reaction?

No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."

I have this symptom. What should I do?

This site cannot assess anyone. A pharmacist or clinician can; for an emergency, call the local emergency number. Nothing on this page is medical advice.

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. Terms are pooled across spelling and capitalisation variants of one MedDRA preferred term. 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.