Pharmacologic class (EPC) · 3 drug pages

Estrogen receptor antagonist: adverse event reports filed with FDA

27,672 reports list a drug in this class as a suspect or interacting product, 2004–2026.

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.

27,672
reports across the class: 0.1% of all reports; 2,106
reports, 12 months to June 2026: 3,489 in the 12 months before; 72.9%
marked serious by the reporter: 57.4% across all reports; 3
drugs with a page: brand and generic names counted separately

Estrogen receptor antagonist is a pharmacologic class (an FDA Established Pharmacologic Class) with 3 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 27,672 adverse event reports received by FDA, 0.1% of the database, from January 2004 to June 2026.

2,106 reports arrived in the 12 months to June 2026, down 40% from 3,489 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 72.9% of the class's reports are marked serious, 14.2% record death among the outcomes and 20.7% record hospitalisation, as reported.

Across the class the reactions recorded most often are malignant neoplasm progression (13.4%), nausea (11.7%) and fatigue (11.6%). The class median share shown beside each term is the middle value across the member drugs; it is the comparison used on every drug page in this class.

The members table is ordered by report count for navigation only. 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."

Drugs in the class

Drug	Name type	Reports	Latest 12 months	Marked serious	Top term recorded
Fulvestrant	generic	11,797	1,335	94.7%	Malignant neoplasm progression
FaslodexFulvestrant	brand	8,884	601	75.9%	Malignant neoplasm progression
OrserduElacestrant	brand	6,991	170	32.4%	Nausea

Ordered by report count for navigation only. 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."

Reports by month, five years

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

Reactions recorded across the class

share of class reports recording the termmedian drug in the class

Malignant neoplasm progression13.4%3,712
Nauseafeeling sick11.7%3,250
Fatiguetiredness11.6%3,211
Deaththe patient died; cause not stated by this term8.2%2,270
Diarrhoealoose or frequent stools6.9%1,922
Metastases to bone6.4%1,763
Vomitingbeing sick5.9%1,636
Disease progressionthe disease advanced5.9%1,624
Neutropenialow neutrophils, a type of white blood cell5.8%1,601
Metastases to liver5.3%1,461
Drug ineffectivethe medicine did not work as expected5%1,383
Painpain, site not specified4.9%1,354
Breast cancer metastatic4.8%1,326
Arthralgiajoint pain4.3%1,202
Astheniaweakness or lack of energy4.3%1,189
Dyspnoeashortness of breath4.2%1,154
Decreased appetitereduced appetite4.1%1,127
Neoplasm progression3.5%965
Rashskin rash3.3%921
Constipationconstipation3.2%876
Off label useused for a purpose or in a way not on the label3.1%854
Headachehead pain3.1%845
Coughcough3.1%844
Malaisegeneral feeling of being unwell3%833
Anaemialow red blood cells2.9%816

Solid bar: share of all class reports. Hollow bar: the median share across the 3 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death14.2%3,929

Life-threatening2.9%806

Hospitalisation (initial or prolonged)20.7%5,731

Disability0.9%256

Congenital anomaly0%8

Other serious53.8%14,893

Not serious27.1%7,489

Patient age

Under 20%3

2 to 110%2

12 to 170%3

18 to 444.5%1,241

45 to 6430%8,306

65 to 7419.5%5,407

75 and over14%3,861

Age not given32%8,849

Who reported

Physician33.2%9,176

Pharmacist3.8%1,044

Other health professional18.9%5,242

Lawyer0%4

Consumer or non-health professional39.2%10,842

Not given4.9%1,364

Grey bar: all 20,646,523 reports in the database. Outcome flags are as the reporter set them and are not verified by FDA.

Questions about Estrogen receptor antagonist reports

Which drugs are in the Estrogen receptor antagonist class on this site?

Fulvestrant, Faslodex and Orserdu. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

27,672 reports through June 2026, 2,106 of them in the latest 12 months. A report listing two drugs of the class counts once for each.

What reactions are recorded most often?

malignant neoplasm progression (13.4%), nausea (11.7%), fatigue (11.6%), death (8.2%) and diarrhoea (6.9%).

Can the members table be used to rank the drugs?

No. 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." Drugs differ in how many people take them, in the conditions they treat, in time on the market and in how diligently reports are collected.

How do I report an adverse event?

Through FDA MedWatch (Form FDA 3500, or 1-800-FDA-1088) or to the manufacturer. See the guide on how to report.

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. A class is the Established Pharmacologic Class most often attached to a drug's reports by openFDA's label harmonisation, or from the NDC Directory where reports carry none. 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.