Over five million Americans suffer from Alzheimer's disease. While a few drugs can temporarily alleviate symptoms, there's no treatment that slows the progression of the underlying disease, so family members watch helplessly as their loved ones' minds fade away. Drug companies are determined to end this suffering. So far, 99 percent of Alzheimer's clinical trials have failed, costing companies billions. Despite these repeated stumbles, firms are undeterred and currently have more than 70 potential Alzheimer's treatments in development.