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Leqembi, the first anti-Alzheimer’s treatment approved in Europe, represents both a scientific breakthrough and a high-stakes gamble. Amid fragile hope, troubling side effects, and limited access, the prospect of a real therapeutic turning point should be treated with caution.

After decades of research and broken promises, the arrival of Leqembi (lecanemab) marks a symbolic milestone in the fight against Alzheimer’s. Developed by Eisai and Biogen, this monoclonal antibody has just been approved in the European Union for the treatment of early-stage Alzheimer’s. For the first time, a drug aims to slow the progression of the disease rather than simply ease its symptoms. But can it truly be called a revolution?

Cautious Hope

Leqembi targets amyloid plaques, abnormal protein deposits in the brain believed to speed up neuronal degeneration. It is given by infusion every two weeks to patients with mild cognitive impairment or early-stage dementia, provided tests have confirmed the presence of amyloid.

The European approval, granted in April 2025, applies only to a subgroup of patients – those who do not carry two copies of the ApoE4 gene, a known risk factor for serious side effects. This caution reflects the risk of brain abnormalities – including swelling and microbleeds, collectively known as ARIA – observed in clinical trials, particularly among patients with two copies of the gene.

When it comes to effectiveness, expectations should be tempered. In the international Clarity AD trial, Leqembi slowed cognitive decline in treated patients compared with those receiving a placebo. The difference, measured on a specialized scale (CDR-SB), amounted to about 27 percent over 18 months. In other words, the treatment does not cure Alzheimer’s or halt the disease, but it can slow its progression in a carefully selected patient group. While statistically significant, this effect remains modest in everyday life for many patients and their families.

The first commercial rollout took place in Austria and Germany, where demand for the treatment is high. Prescribing Leqembi, however, is strictly regulated – it requires tests to confirm the presence of amyloid, regular MRI scans to monitor potential complications, and close follow-up.

Progress, but No Miracle

Side effects remain the main concern. Studies report cases of brain swelling or microbleeds in a notable proportion of patients – up to 13 percent for ARIA-E – as well as infusion reactions and, more rarely, serious events requiring treatment discontinuation. The safety profile justifies the enhanced monitoring mandated by health authorities.

Moreover, Leqembi is intended only for patients at a very early stage of the disease – it is not approved for moderate or advanced forms. Identifying eligible patients relies on sophisticated diagnostic tools, which are not widely available in some healthcare systems. The cost of the treatment, which has yet to be established in many countries, may also limit access in the short term.

Despite these limitations, the arrival of Leqembi marks a meaningful advance: it is the first time a European authority has recognized a drug capable of targeting a central mechanism in Alzheimer’s. This offers renewed hope for research and opens the door to other targeted therapies.

Caution, however, remains key. Many experts stress the importance of continuing research, improving early diagnosis, and ensuring comprehensive support for patients. Leqembi is neither a miracle nor a solution for everyone, but it is a promising step toward better understanding and managing this complex disease.

For the patients affected, hope remains. For society, the fight against Alzheimer’s goes on – driven as much by prevention and compassionate care as by medical innovation.