85/100 · Critical
Manufactured by Novartis Pharmaceuticals Corporation
Letrozole Adverse Events: High Serious Reaction Rate, Primarily in Older Females
148,871 FDA adverse event reports analyzed
Last updated: 2026-05-12
LETROZOLE is a medication tracked in the FDA Adverse Event Reporting System (FAERS), manufactured by Novartis Pharmaceuticals Corporation. Based on analysis of 148,871 FDA adverse event reports, LETROZOLE has a safety score of 85 out of 100. This score indicates a relatively favorable safety profile, with fewer or less severe adverse events compared to many other tracked medications. The most commonly reported adverse reactions for LETROZOLE include FATIGUE, NAUSEA, NEUTROPENIA, DIARRHOEA, MALIGNANT NEOPLASM PROGRESSION. This page provides a comprehensive breakdown of reported side effects, safety signals, patient demographics, and AI-powered safety analysis for LETROZOLE.
Letrozole has a safety concern score of 85 out of 100, placing it in the high concern category based on analysis of FDA adverse event data. The FDA has received approximately 148,871 adverse event reports for this medication, which is primarily manufactured by Novartis Pharmaceuticals Corporation.
The most commonly reported adverse events include Fatigue, Nausea, Neutropenia. Of classified reports, 80.4% were designated as serious by the FDA, meaning they involved hospitalization, disability, or other significant medical outcomes. Letrozole reports show a high rate of serious adverse events, particularly fatigue, nausea, and neutropenia.
The majority of reports are from older female patients, with a significant number of serious outcomes. Pain and disease progression are also commonly reported, indicating potential long-term health impacts.
Patients taking Letrozole should monitor for the commonly reported side effects and contact their healthcare provider if they experience any unusual symptoms. Letrozole can cause serious adverse events such as neutropenia and anemia, and patients should be monitored closely, especially for signs of infection or bone marrow suppression. Drug interactions, particularly with other cytotoxic agents, should be This analysis is based on voluntary FDA adverse event reports and should not replace professional medical advice.
Letrozole received a safety concern score of 85/100 (high concern). This is based on a 80.4% serious event ratio across 59,008 classified reports. The score accounts for 148,871 total adverse event reports and 100 distinct reaction types. This high score reflects a significant proportion of serious adverse events in the reporting data.
Adverse event reports by sex: Female: 54,310, Male: 837, Unknown: 71. The most frequently reported age groups are age 70 (1,281 reports), age 63 (1,242 reports), age 65 (1,202 reports). These demographics reflect reporting patterns and may not represent the full patient population.
Out of 59,008 classified reports for LETROZOLE:
The FDA classifies an adverse event as “serious” if it results in death, hospitalization, disability, congenital anomaly, or requires intervention to prevent permanent damage.
Demographics reflect voluntary FDA adverse event reporting patterns and may not represent the full patient population.
Letrozole can cause serious adverse events such as neutropenia and anemia, and patients should be monitored closely, especially for signs of infection or bone marrow suppression. Drug interactions, particularly with other cytotoxic agents, should be
If you are taking Letrozole, here are important things to know. The most commonly reported side effects include fatigue, nausea, neutropenia, diarrhoea, malignant neoplasm progression. While many of these may be mild and temporary, you should contact your healthcare provider if any symptoms are severe or persistent. Patients should inform their healthcare provider of any new or worsening symptoms, especially signs of infection or changes in blood counts. Regular blood tests are recommended to monitor for potential adverse effects. If you experience a serious adverse reaction, seek emergency medical attention immediately or call 911. You can report side effects to the FDA's MedWatch program at 1-800-FDA-1088.
The FDA continues to monitor letrozole safety, and updates are regularly provided. Healthcare providers should report any adverse events to the FDA's MedWatch program.
The FDA has received approximately 148,871 adverse event reports associated with Letrozole. These reports come from healthcare professionals, consumers, and manufacturers through the FDA Adverse Event Reporting System (FAERS). Note that the number of reports does not directly indicate the frequency of side effects, as adverse events are voluntarily reported and may be underrepresented.
The most frequently reported adverse events for Letrozole include Fatigue, Nausea, Neutropenia, Diarrhoea, Malignant Neoplasm Progression. By volume, the top reported reactions are: Fatigue (7,159 reports), Nausea (5,258 reports), Neutropenia (4,896 reports). These figures reflect FDA adverse event reports and may not represent the true incidence rate of these side effects in all patients taking Letrozole.
Out of 59,008 classified reports, 47,448 (80.4%) were classified as serious and 11,560 as non-serious. The FDA classifies an event as "serious" if it results in death, hospitalization, disability, or other medically significant outcomes. A higher serious-event ratio warrants closer attention but does not necessarily mean the drug is unsafe.
Adverse event reports for Letrozole break down by patient sex as follows: Female: 54,310, Male: 837, Unknown: 71. This distribution reflects reporting patterns rather than actual risk differences between groups. Reporting rates can be influenced by prescribing patterns, disease demographics, and reporting behavior.
The most frequently reported age groups for Letrozole adverse events are: age 70: 1,281 reports, age 63: 1,242 reports, age 65: 1,202 reports, age 62: 1,191 reports, age 61: 1,185 reports. Age-related reporting patterns can reflect both the demographics of the patient population and potential age-related susceptibility to certain side effects.
The primary manufacturer associated with Letrozole adverse event reports is Novartis Pharmaceuticals Corporation. Multiple manufacturers may produce generic versions of this drug. The manufacturer listed reflects the most frequently reported brand in FDA adverse event data.
Beyond the most common reactions, other reported adverse events for Letrozole include: Arthralgia, White Blood Cell Count Decreased, Alopecia, Pain, Asthenia. Less common side effects can still be clinically significant. Patients should report any unusual symptoms to their healthcare provider.
You can report adverse events from Letrozole to the FDA through their MedWatch program at www.fda.gov/medwatch, by calling 1-800-FDA-1088, or by completing Form FDA 3500. Healthcare professionals, consumers, and manufacturers can all submit reports. Reporting helps the FDA monitor drug safety after approval.
Letrozole has a safety concern score of 85 out of 100 (high concern). This score is calculated from the ratio of serious to non-serious adverse events, the diversity of reported reactions, and the overall volume of reports relative to usage. Letrozole reports show a high rate of serious adverse events, particularly fatigue, nausea, and neutropenia.
Key safety signals identified in Letrozole's adverse event data include: High rate of serious adverse events (80.4%). Common reactions include fatigue, nausea, and neutropenia. Significant number of reports related to disease progression and metastases. These signals are derived from patterns in FDA reports and should be discussed with a healthcare provider for personalized assessment.
Letrozole can cause serious adverse events such as neutropenia and anemia, and patients should be monitored closely, especially for signs of infection or bone marrow suppression. Drug interactions, particularly with other cytotoxic agents, should be Always inform your healthcare provider about all medications, supplements, and over-the-counter drugs you are taking before starting Letrozole.
Patients should inform their healthcare provider of any new or worsening symptoms, especially signs of infection or changes in blood counts. Regular blood tests are recommended to monitor for potential adverse effects.
Letrozole has 148,871 adverse event reports on file with the FDA. The majority of reports are from older female patients, with a significant number of serious outcomes. The volume of reports for Letrozole reflects both the drug's usage level and the vigilance of the reporting community.
The FDA continues to monitor letrozole safety, and updates are regularly provided. Healthcare providers should report any adverse events to the FDA's MedWatch program. For the most current regulatory information, check the FDA's drug labeling database or consult your pharmacist.
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