Plot hole: If Bradley Cooper was able to "quintuple" his money every day in the market as he claims to have done, he would have been able to earn the $100k he borrowed from a loan shark within a few days, starting from $800. Alternatively, he is shown in one scene winning a pot in poker where he could presumably also make a large amount of "seed" money from gambling. There was no need to borrow such a small sum of money from a loan shark, making the entire sub-plot unnecessary.
Plot hole: NZT makes Eddie hyper-aware of everything and allows him to access all memories in his brain, so he is able to make highly intelligent decisions and outsmart others. He somehow fails to realise how reckless he is being when he originally makes over $2 million in the stock market (and also wins at the casino) and the attention it would draw to him. He made himself a huge target for others, some of whom would know he was on NZT, but somehow was clueless about this while being aware of everything else.
Suggested correction: The main character says he did quintuple his money four days in a row, not that he could continue to do so. "Presumably" he could do anything, like robbing a bank. Gambling is not a secure source of income, even with knowledge of the odds and every tell, he could also lose a lot of money.
He takes the seed money and then goes on to make a couple million with it on the stock market. There's really no reason he couldn't have just done that with the $800 seed money (also what the hell happened to that $10-20k stack of cash he took from Vernon's apartment? Somehow that was dwindled down to only $800?). The time constraint was totally artificial. He didn't need to conquer the world in 2 months except for the needs of the plot.