OK, so scientists have found a great new substance: That substance makes you think ten times as fast! The advantages are obvious. However, as every medicine, this pill will have side effects.
There are obvious side effects like that a faster-thinking brain will likely also have a much higher energy consumption. However, there may also be less obvious side effects from the mere facts that you're still communicating with other humans who have a normal thinking speed, and interact with a world (including your own body) that didn't speed up with your own thinking.
So my question: How would your thinking speed-up affect your life? Could those side effects even be so severe that you'd not want to use the pill, except possibly for rare extreme conditions?