Sales of Leqembi (lecanemab), a drug that targets Alzheimer’s disease, have been climbing steadily since its approval by the U.S. Food and Drug Administration (FDA) in 2023. In the last quarter of 2024 alone, it brought in $87 million USD.
The drug is only the second treatment approved in the U.S. that aims to modify the course of Alzheimer’s, rather than just easing symptoms.
In a major Phase 3 clinical trial, lecanemab showed it could slow the decline in memory and thinking ability by 27% overall in people with early Alzheimer’s. This helped convince an FDA advisory panel to vote unanimously that the drug had clear clinical benefits.
However, a closer look at the trial data revealed something unexpected: women seemed to benefit far less from the drug than men, with one subset of the data suggesting little to no improvement for female patients. This raised questions in the medical community about whether Leqembi should be prescribed as widely to women.
To find out if this potential sex difference in how the drug works was real or just a fluke in the data, Daniel Andrews, a Ph.D. student at McGill University, worked with a team led by neuroscientist Prof. Louis Collins.
They used real-world data from Alzheimer’s patients that was publicly available and created computer simulations that mirrored the same characteristics and rules used in the original lecanemab trial. This allowed them to test the results without needing to run a new live trial.
Their analysis confirmed that lecanemab likely worked better in men than in women during the Phase 3 trial. But the researchers also found that the evidence was not strong enough to say the drug doesn’t work in women at all. In other words, lecanemab may still offer some benefit to female patients—it just might not be as noticeable or consistent as it is for males.
The study, published in the journal Alzheimer’s & Dementia, also highlighted a key concern: in some patients, lecanemab causes serious side effects, which makes it especially important for doctors to weigh the risks and benefits carefully—particularly when prescribing the drug to women, who may see fewer improvements.
These new findings could help doctors make better, more personalized treatment decisions and may influence whether countries outside the U.S. choose to approve lecanemab. The results also point to a bigger issue in drug development: the need to better account for sex differences in clinical trials.
Review and Analysis
This study sheds light on an important—and often overlooked—issue in medicine: how biological sex can affect how well a drug works. While lecanemab clearly benefits some people with early Alzheimer’s, this research shows the effect may not be equal for everyone, especially when it comes to women.
This is not the first time researchers have noticed that women and men may respond differently to certain medications. But the lecanemab case is notable because Alzheimer’s disease affects more women than men. If a new drug is less effective in the group most likely to need it, that’s a serious concern.
The researchers didn’t conclude that women should stop taking the drug, but they stressed that more work is needed to understand how well it works in different groups of people. They also highlighted how future drug trials can improve by designing studies that pay closer attention to sex-related differences from the start, instead of analyzing them afterward.
As lecanemab continues to roll out globally, this study may help guide doctors in making more informed decisions about who should take it, especially when weighing the benefits against the potential harms.
It also reminds us that “one-size-fits-all” solutions in medicine don’t always work—and that tailoring treatments to individual patients, including by sex, may lead to better outcomes.
If you care about Alzheimer’s, please read studies about the likely cause of Alzheimer’s disease , and new non-drug treatment that could help prevent Alzheimer’s.
For more information about brain health, please see recent studies about diet that may help prevent Alzheimer’s, and results showing some dementia cases could be prevented by changing these 12 things.
The research findings can be found in Alzheimer’s & Dementia.
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