The story takes place in a modern setting and I think it takes place mostly in a suburb. The characters find pills that I believe accidentally ended up on earth by aliens. The pills would enabled whoever consumed them to think they were a famous person and perform a task that they were known to do with complete mastery.
The downside to the pills was that you had no idea how long they would last for, and you didn't remember what you did while under the influence of it. Which means that you could be crossing a tight rope while hundreds of miles in the air, and the pill could stop working.
I believe there were three main characters: two were boys and one was a girl. I don't remember what the conflict was in the story, but I remember liking it and I remember it was a pretty long book (I think 300+ pages). Thank you if you know this story.
Edit: If it helps, I remember reading the book in either middle school or highschool. I remember that it didn't contain chapters but parts. The parts were used in place of chapters, but each part was really long. There were either 3 or 4 parts to the story. The main characters were either kids or teenagers. One scene that comes to mind involved one of the characters entering their friend's kitchen and he was either on a counter or chair juggling some objects. Not too long after entering, the boy lost the ability to stop juggling. The girl makes a statement that she notices that each pill varies in how long they affect the user: Sometimes a few minutes and other times much longer. Finally, I remember the cover being a cartoon cover. Hopefully that helps.