MedDRA preferred term

On and off phenomenon: adverse event reports recording this term

5,199 reports to FDA record it, 2005–2026; 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.

5,199
reports recording the term: 0% of all reports; 987
reports, 12 months to June 2026: 655 in the 12 months before; 87.8%
marked serious by the reporter: 57.4% across all reports; 5.9%
record death among outcomes, as reported: 9.1% across all reports

"On and off phenomenon" is a MedDRA preferred term recorded in 5,199 adverse event reports received by FDA, 0% of the database, from May 2005 to June 2026. The term is chosen by whoever codes the report to match what the reporter described.

987 reports recorded it in the 12 months to June 2026, up 51% from 655 in 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, 87.8% are marked serious, 5.9% include death among the outcomes and 51.8% include hospitalisation, as reported.

The drugs listed most often as suspect products in those reports are Carbidopa levodopa, Duodopa and Foscarbidopa/foslevodopa. 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
Carbidopa levodopa	Aromatic amino acid	2,084	10.3%
Duodopa	—	1,187	6.8%
Foscarbidopa/foslevodopa	—	759	16.2%
Duopa	Aromatic amino acid	237	2.8%
Vyalev	—	202	7.7%
Rytary	Aromatic amino acid	120	1.2%
Pramipexole	Nonergot dopamine agonist	99	2.5%
Clozapine	Atypical antipsychotic	88	0.1%
Inbrija	Aromatic amino acid	72	1.2%
Apokyn	Dopaminergic agonist	67	1.3%
Carbidopa and levodopa	Aromatic amino acid	64	2.7%
Levodopa	Aromatic amino acid	63	4.4%
Amantadine	Influenza A M2 protein inhibitor	62	2.8%
Ropinirole	Nonergot dopamine agonist	59	2.1%
Entacapone	Catechol-O-Methyltransferase inhibitor	58	6%
Nourianz	—	56	1.1%
Rivastigmine	Cholinesterase inhibitor	55	2.1%
Sinemet	Aromatic amino acid	55	1.2%
Nuplazid	Atypical antipsychotic	54	0.1%
Neupro	Nonergot dopamine agonist	45	0.7%
Quetiapine	Atypical antipsychotic	43	0.1%
Mirtazapine	—	29	0.1%
Pramipexole dihydrochloride	Nonergot dopamine agonist	29	1.8%
Benserazide Hydrochloride Levodopa	—	28	4.1%
Stalevo	—	27	1%

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
Aromatic amino acid	2,695	5.1%	2.7%
Nonergot dopamine agonist	258	1.3%	1.4%
Atypical antipsychotic	217	0%	0%
Dopaminergic agonist	104	1.6%	2.2%
Influenza A M2 protein inhibitor	91	2%	2%
Catechol-O-Methyltransferase inhibitor	79	3.9%	4%
Cholinesterase inhibitor	60	0.2%	0%
Factor Xa inhibitor	36	0%	0%
Monoamine oxidase inhibitor	33	0.5%	0.2%
Benzodiazepine	32	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 20%0

2 to 110%2

12 to 170.1%5

18 to 441%53

45 to 6415.5%804

65 to 7429.6%1,538

75 and over23.2%1,207

Age not given30.6%1,590

Patient sex

Female40.8%2,123

Male56.2%2,924

Not given2.9%152

Grey bar: all 20,646,523 reports in the database. 17.1% of these reports give the United States as the country.

Questions about "On and off phenomenon"

What does "On and off phenomenon" 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 on and off phenomenon?

5,199 reports through June 2026 (0% of all reports), 987 of them in the latest 12 months.

Which drugs appear most often in these reports?

Carbidopa levodopa (2,084), Duodopa (1,187), Foscarbidopa/foslevodopa (759), Duopa (237) and Vyalev (202). 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.