Off-label use of stimulants, such as Ritalin, is on the rise among college students. Studies show that 5 percent to 15 percent of students use prescription drugs as study aids, and surveys suggest the practice may be common among academics as well. The trend has sparked debates over how and when these cognitive enhancers should be used. Military personnel routinely use stimulants while on active duty, but should that practice also be permitted among surgeons working long shifts? What about scientists working late nights in the lab? Or students taking exams?