Which Cognitive Enhancers Should Be Legal?

Many scientists are coming out in favor of making it legal for people to use "cognitive enhancers," drugs that make us more productive workers by increasing attention spans, aiding memory, and making us more alert. Over the weekend, a group of prominent researchers published an op-ed in Nature outlining how to make cognitive enhancers legal and safe. What do you think? Take our poll.

Which kinds of drugs do you think should be made legal as cognitive enhancers? Remember, these drugs will be administered by doctors, so some of the problems with impurities and addiction you get with black market versions of these drugs can be avoided.