For whatever reason, I got to go to a pre-screening of the movie
Limitless, and cognitive enhancement is central to the plot. Without revealing to much, the film is about a man who finds a drug that makes him incredibly smart and then some shenanigans happen. The science in the film is nonexistent, but this wont stop me from trying:
The Science :
The explanation for how the pill works is bogus, but the mechanism is not really central to the film. For reference, the myth that we only use 20% of our brains is meaningless, we usually use 100% of our brain's capacity, though not all neurons fire at once. 100% of the neurons firing would actually constitute a possibly fatal seizure. Cognitive enhancement would involve tweaking the way the brain works, not recruiting more neurons.
The effects of the hypothetical drug were close to those of existing drugs. We see an amphetamine like speeding of thought and focus, and improved recall, and also some aspects of mania, recklessness, and blackouts. I would say that all of these effects might be obtained by some of the existing hallucinogenic amphetamines, or something close too it. Indeed, I would say nothing out of the realm of the possible for the first several scenes.
It's initially unclear whether the scenes depict how the protagonists feels subjectively, or the objective effects of the drug. Much of the confidence, energy, and euphoria could be written off as if the effects of the drug merely altered how intelligent you feel rather than how intelligent you actually are.
The drug boosts our protagonist's abilities far beyond even the upper abnormal range. I believe there is an upper limit to what you can do with a fixed number of neurons, and would not expect any drug to actually make you much better than the best humanity has to offer. Now, maybe we could boost intelligence up to this abnormal intelligence range.
The protagonist becomes better at fighting by taking the drug. This doesn't make sense: coordination uses "muscle memory", which is a non conscious system of reflexes and fast non-conscious computation. You can't consciously control this system, it needs to be trained. Of course, we know that some drugs can alter how you control your strength and perceive pain, maybe you don't need muscle-memory to be good at self defense.
At one point the protagonist gets more of the drug by drinking blood from someone who had injected the substance. This ( and it should be obvious ) doesn't make medical sense. The drug would be too dilute. Unless of course, by injecting the drug you trigger some metabolic modification that increases potency 1000-fold by a mechanism normally impossible if ingested, but stable and resistant to degradation by ingestion after the fact. The last sentence made no sense, didn't it ? If you see the film you will see what I mean. As far as the film goes, the awkwardness of the plot surrounding this scene trumps any departure from medical reality.
tl;dr: The nature of the drug's effects are reasonable, but their magnitudes aren't. There are some plot holes which matter more than inaccurate science.
The Philosophy :
The film was more of an action/drama/comedy than a serious philosophical exploration of the meaning of human enhancement. I won't enumerate existing philosophical questions here, since this stuff is already heavily debated elsewhere on Spacecollective. Lets just say that access to enhancement was not evenly distributed in the film, giving some people clear advantages. Of course, the world already works much the same way with unequal access to education, resources, and capital. Many social problems surrounding enhancement are age-old social problems that seem novel in light of new technologies.
summary: it's a movie, it's decent, but it isn't at the frontier of exploring the possibilities for and implications of human enhancement.