These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Ass Pull: At the end of the movie Eddie got off the drugs offscreen, but retained all the capabilities. Why? Because he came up with Phlebotinum offscreen.
It's possible that he hasn't retained all of his capabilities, but has managed to hold on to some of them while turning his life around unmedicated. It's also possible that he actually *was* still on NZT, and that final dialogue was really just a huge gamble to buy him time and get Van Loon off his back.
The alternate ending of the movie has him acting a lot more hostile and less composedly to van Loon, indicating that he is in fact lying.
He actually states that he realized the weaknesses of NZT, so he just made it so the effects became permanent.
After everything that Eddie did on NZT, it is completely believable that while on it, he identified and corrected the weakness, or even made its effects permanent.
Fridge Brilliance: The film uses some common scientific myths, such as Vernon's statement of 90% of Your Brain and when Eddie mentions his Improbably High IQ of four digits. Vernon is a drug dealer with no scientific credentials at all, and was simply explaining things in a simple, if inaccurate, manner. Eddie never took any IQ tests, and just pulled some random number out of his ass.
Fridge Logic: Why didn't the police search Eddie at the murder scene? If he was a prime suspect, which he would be having found the body, they would have cuffed and searched him before taking him to the police department to make a statement and therefore have found the NZT pills he shoved into the small of his back.
Usually the person that calls the cops in the first place to report a dead body isn't treated as the prime suspect.
Eddie described his ex-wife Melissa as the smartest woman he knew who dumped him immediately. High intelligence and impulsive behavior. Those sound like indications that she was already on NZT when he met her.
When Lindy takes NZT to escape from an assassin, she uses a little girl as an Improvised Weapon. When she is free of the effects, she doesn't want anything to do with NZT or Eddie.
Any other user hooked on NZT is willingly enough to torture or kill for another dose.
One-Scene Wonder: Johnny Whitworth as the delightfully sleazy Vernon Gant, the man who introduces Eddie to NZT. He is killed fifteen minutes into the movie. Also, Eddie's bodyguards who also last only two scenes.
Squick: Not just the aforementioned Eye Scream but what comes shortly before that, to which everyone in the audience went "Oh, EWWW!"
What an Idiot: Eddie's new and improved life is interrupted when he finds all his NZT-48 is gone. For the month he's been taking those limited supply of drugs (including double doses), did Eddie not think to ration them properly? That's a mistake that anyone, with or without heightened intelligence, wouldn't overlook.
It was stolen. He didn't run out. If you're thinking of the scene when he calls in sick before the big meeting, he deliberately didn't take more because he thought he killed that woman while under NZT's influence.
He didn't find out about the dead girl until after we went to the meeting "sober". He didn't take them because he didn't like that he kept missing time.