What are the side effects of Lecanemab, Biogen's newly approved alzheimer's drug?

Photo by Jean Vella

Lecanemab was just recently approved for clinical use through a rush approval process. But what are the side effects? First of all, there were a lot of study participants over an 18-month period and they are alzheimer’s patients which basically means they’re sick with a terminal disease so you expect some adverse events. The way side effects are identified is by looking at how many more adverse effects you see in the treatment group vs. the placebo group. If there were zero side effects, you’d see a treatment group that had roughly the same fatality and disease rate as the placebo group. That is certainly not the case with Lecanemab—this drug can hurt you!

Biggest side effects

In what follows I review the reported results from the clinical trial. You can access the paywalled report here and if you’re lucky you can get the full paper for free here.

Brain swelling (ARIA-E)

Excess fluid build up causes excess pressure on the brain. Symptoms of this problem include headaches, nausea, vomiting, seizures, drowsiness, visual disturbances and dizziness (if it doesn’t kill you or put you in a coma). In the trial, brain swelling occurred in 113 (12.6%) people who received the treatment but only 15 (1.7%) people in the placebo group. That’s a bad side effect and a high rate of occurence.

Bleeding in the brain (ARIA-H)

Another really bad side effect. These very tiny releases of blood but they can add up if you have a lot of them. This issue affected 155 (17.3%) of the treatment group but only 81 (9.0%) of the placebo group.

Superficial siderosis

A toxic, debilitating build up of iron in the tissues between brain and skull. The build up is caused by bleeding in the brain over time. It often manifests by abnormal uncoordinated movements and hearing loss. In the treatment group, this affected 50 (5.6%) patients but only 22 (2.5%) in the placebo condition.

Conclusions

These side effects are severe, unfortunate, and common. Patients and their family members should know the risks and weigh them carefully before leaping in. In many cases the drug caused much more harm than good. We all want to see alzheimer’s disease cured but the cost in terms of side effects is very high in this case. It’s definitely good to be cautious.