Infusion reactions: About a quarter of patients will experience a mild infusion reaction. Symptoms might include fever, headache, rash, nausea or abdominal discomfort. These symptoms can usually be controlled with medications such as Tylenol of Benadryl if necessary. Amyloid related imaging abnormalities (ARIA): ARIA is a condition that indicates swelling or bleeding in the brain. This occurs in about 2 in 10 people receiving lecanemab, though most often causes no symptoms and resolves without any treatment. However, more severe cases can occur, leading to symptoms such as headache, confusion, visual changes, dizziness, nausea and seizures. In rare cases, this can lead to death. Because of the risk of bleeding, this medication is not recommended for patients receiving strong blood thinners. Also, those receiving lecanemab should not receive clot-busting medications.