Eli Lilly has halted two late-stage clinical trials for its experimental Alzheimer's treatment semagacestat, after it worsened patients' symptoms and increased their risk for skin cancer. Semagacestat was designed to block an enzyme in the brain that prompts the formation of amyloid plaque, the buildup of which is widely believed to cause Alzheimer's. However, an interim analysis of the trials analyzing the drug's effectiveness in 2,600 patients showed that cognition and ability to execute daily tasks deteriorated more in participants taking the drug than in those taking a placebo.