Leqembi (lecanemab) Interactive Dashboard for Adverse Events Reports

June 7, 2026

This interactive report with 10 pages summarizes more than 3,000 adverse event cases for Leqembi (lecanemab) reported to the FDA's Adverse Events Monitoring System (AEMS) through June 5, 2026. Each chart has interactive filters; click on values and other charts on the page will adjust based on the filters you selected. You may sort by column headers in most cases. The last page of this report has a summary of cases and outcomes for the newest Leqembi product (approved in August 2025) called Leqembi IQLIK which is administered subcutaneously instead of by intravenous infusion.

More about Leqembi:

FDA issued a drug safety communication about Leqembi on August 28, 2025. They are recommending an earlier magnetic resonance imaging (MRI) monitoring prior to the 3rd infusion for patients with Alzheimer’s disease taking Leqembi (lecanemab) so they can identify cases of ARIA (described below) earlier. The FDA says that Identifying patients with ARIA-E can lead health care professionals, patients, and their families to delay or discontinue Leqembi treatment to potentially mitigate these serious and, in some cases, fatal events.

A few highlights from the reports above from FAERS:

> Most (62%) of the of the 3,215 reported events were considered “non-serious.” However, this is a decrease from a year ago, when 72 % of the 2,126 reports were considered non-serious.
> Some cases of Amyloid Related Imaging Abnormalities (ARIA, which is described below) are very serious, while others are asymptomatic or resolve. This explains why some of the ARIA cases are designated as "serious" or "nonserious."
> 100 of the patients died. - about 650 of the patients were hospitalized.
> The most common adverse reactions are, in declining order: Headache, ARIA with swelling, ARIA with bleeding, infusion-related reactions, and chills. - Most of the events happened in the U.S. or Japan.
> For patients taking multiple drugs (concomitant drugs with Leqembi) the drug list for each case is provided. In the interactive table, you may filter for a concomitant drug and view the associated outcomes for the cases where the drug was being taken along with Leqembi.

Leqembi (lecanemab), a monoclonal antibody drug, was approved in January 2023 as a treatment for patients in the early stages of Alzheimer’s, including those with mild cognitive impairment or mild dementia. Alzheimer’s disease is an irreversible, progressive brain disorder that slowly destroys memory and thinking skills and, eventually, the ability to carry out simple tasks. The drug works by slowing the progression of the disease by reducing the number of amyloid plaques (thought to be a contributing factor to Alzheimer’s) in the brain.

Leqembi was developed jointly by U.S.-based Biogen and Japan’s Eisai. In April 2025, it was approved for use in the European Union. Eisai reports that it is also approved in U.S., Japan, China, South Korea, United Kingdom, Mexico, and more, and is under regulatory review in 14 countries and regions. Recently, the approval has been rejected in Australia. Since being on the market for about two years, Eisai estimates that around 13,500 U.S. patients have taken it. This represents a tiny percentage of patients with Alzheimers; the FDA estimates that around 7 million Americans are living with Alzheimer’s.

In January 2025, the boxed warning was modified to add that the severe side effect of ARIA (Amyloid Related Imaging Abnormalities) can be fatal. ARIA-E (for edema/effusion) often includes temporary swelling in areas of the brain. It usually occurs early in treatment and is asymptomatic, although serious and life-threatening events like seizures can occur.

In August 2025, the FDA approved an auto-injector subcutaneous formulation (Leqembi IQLIK) that patients can use at home as a weekly maintenance therapy after 18 months of intravenous (IV) initiation treatment every two weeks. Optionally, after the 18 months they may continue with infusions every four weeks for maintenance therapy. Eisai and Biogen are aiming to get the subcutaneous formulation approved for once-weekly initiation therapy, which could be a more convenient option for most patients. The FDA is expected to take action by August 2026.

The FDA provides a drug trials snapshot that describes the demographics of the participants in the clinical trial that led to Leqembi’s approval. The trials snapshot reports that men experienced better results with Leqembi than did women, although the sample size was too small to make broader conclusions about effectiveness.

Read our newsletter article on Leqembi for "Fast Facts" about the drug and reasons its approval was controversial. Please contact us with questions or comments about this new dashboard.