MedDRA preferred term · unusual behaviour

Abnormal behaviour: adverse event reports recording this term

39,039 reports to FDA record it, 2004–2026; 0.2% 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.

39,039
reports recording the term: 0.2% of all reports; 1,263
reports, 12 months to June 2026: 1,164 in the 12 months before; 72.5%
marked serious by the reporter: 57.4% across all reports; 5.1%
record death among outcomes, as reported: 9.1% across all reports

39,039 reports in FDA's adverse event database record the MedDRA term "Abnormal behaviour" (in plain words, unusual behaviour): 0.2% of all reports received between January 2004 and June 2026. Coders pick the term that best matches the reporter's description.

1,263 reports recorded it in the 12 months to June 2026, close to the 1,164 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, 72.5% are marked serious, 5.1% include death among the outcomes and 30.9% include hospitalisation, as reported.

The drugs listed most often as suspect products in those reports are Chantix, Nuplazid and Singulair. 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
Chantix	Partial cholinergic nicotinic agonist	1,609	2.3%
Nuplazid	Atypical antipsychotic	1,489	2.8%
Singulair	Leukotriene receptor antagonist	920	4.9%
Tamiflu	Neuraminidase inhibitor	900	6.8%
Abilify	Atypical antipsychotic	762	1.4%
Cymbalta	Serotonin and norepinephrine reuptake inhibitor	741	1.4%
Strattera	Norepinephrine reuptake inhibitor	698	4.4%
Ambien	gamma-Aminobutyric acid A receptor positive modulator	674	7.7%
Seroquel	Atypical antipsychotic	613	1.2%
Lyrica	—	575	0.5%
Risperidone	Atypical antipsychotic	525	1.2%
Levetiracetam	—	459	0.9%
Risperdal	Atypical antipsychotic	448	0.8%
Clonazepam	Benzodiazepine	430	1.1%
Clozapine	Atypical antipsychotic	430	0.6%
Olanzapine	Atypical antipsychotic	425	0.9%
OxyContin	Opioid agonist	425	0.3%
Quetiapine	Atypical antipsychotic	415	0.8%
Montelukast	Leukotriene receptor antagonist	403	3.1%
Gabapentin	Anti-epileptic agent	389	0.5%
Relenza	Neuraminidase inhibitor	387	18.7%
Keppra	—	383	1.5%
Aripiprazole	Atypical antipsychotic	372	1.2%
Zoloft	Serotonin reuptake inhibitor	371	1.7%
Zyprexa	Atypical antipsychotic	365	1.4%

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 0.2% 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
Atypical antipsychotic	7,568	1.1%	0.9%
Serotonin reuptake inhibitor	2,486	0.9%	0.7%
Opioid agonist	2,455	0.3%	0.2%
Benzodiazepine	2,251	0.9%	0.9%
Anti-epileptic agent	2,107	0.8%	0.7%
Central nervous system stimulant	1,965	1.8%	1.1%
Partial cholinergic nicotinic agonist	1,642	2.3%	1.9%
Serotonin and norepinephrine reuptake inhibitor	1,511	0.9%	0.5%
Leukotriene receptor antagonist	1,481	3.8%	3.1%
Neuraminidase inhibitor	1,320	6.5%	3.8%

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%402

2 to 1112%4,695

12 to 175.5%2,136

18 to 4416.7%6,503

45 to 6413.9%5,437

65 to 745.8%2,263

75 and over7.9%3,088

Age not given37.2%14,515

Patient sex

Female41.9%16,358

Male50.3%19,649

Not given7.8%3,032

Grey bar: all 20,646,523 reports in the database. 62.1% of these reports give the United States as the country.

Questions about "Abnormal behaviour"

What does "Abnormal behaviour" mean in an adverse event report?

In plain language: unusual behaviour. 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 abnormal behaviour?

39,039 reports through June 2026 (0.2% of all reports), 1,263 of them in the latest 12 months.

Which drugs appear most often in these reports?

Chantix (1,609), Nuplazid (1,489), Singulair (920), Tamiflu (900) and Abilify (762). 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.