LY-450139, also known as Semagacestat, is a small molecule drug with a maximum clinical trial phase of III and has 1 investigational indication. It was designed to reduce the production of beta-amyloid (Aβ) peptides, which are thought to be involved in the development of Alzheimer's. However, a phase 3 trial was halted early due to the drug's ineffectiveness and potential for harm.