Several modern works of fiction have focused on this question, including Wired and the movie Limitless, which itself was based on another book called The Dark Fields.
Both of them start with a premise that's fundamentally rooted in reality, which is that the road from scientific discovery to mass production is a very long one, and quantities would initially be very scarce. This would quite likely create cut-throat competition of the most literal kind.
Making us 10x smarter would probably not make us any less selfish, which means that there would be a strong motivation for early users to try to cut off access by anyone else, in order to preserve their advantage. Moreover, with extreme intelligence they would likely have no trouble manipulating politicians, media, or even organized crime into unwittingly doing their dirty work for them.
There might be real side effects at first, but if you took a team of neuroscientists and geneticists and supercharged their own brains, even for a short time, they could almost certainly devise ways to improve the drug to eliminate or at least regulate those side effects. Something like this happens in both of the aforementioned plots. In a rational-but-selfish world, normal people would probably be deterred from taking the pill due to a general lack of availability, extraordinarily high expense, a ton of misinformation regarding the real effects and side effects, and a potentially legitimate concern over the quality (as there is with many illegal drugs today - the drug itself might be almost completely safe in its pure form, but you can never really trust the source to be giving you that).
Presuming there were already-intelligent, informed observers who believed they could reliably obtain any quantity of this miracle drug, the main side effect would be painting a giant target sign on your back. You'd be chased around the world by people either (a) wanting to find out your source, (b) trying to stifle the supply and prevent a "leak", and/or (c) morally or religiously opposed to everything you're doing. Being 10x smarter might not be preferable to having 10,000x as many enemies.
There could be physiological side effects, but one thing that probably wouldn't happen would be amphetamine-like symptoms. Amphetamines work by ramping up certain neurotransmitters; they don't literally make the user's brain faster, they are still operating at roughly the same 20 Hz as everyone else. A drug that could literally increase intelligence (AKA "thinking speed") would probably alter glial cells, like astrocytes or Schwann cells. Messing with these could be very dangerous, as we already know of several disorders related to them.
Peripheral neuropathy seems like a likely candidate for a temporary or permanent "comedown". This includes fairly scary conditions such as Guillain–Barré syndrome, Vasculitis, or something more straightforward like kidney failure.
Of course, you might be less lucky and suffer damage to the CNS rather than the PNS. Migraines, epilepsy, bipolar disorder or Alzheimer's - with a drug that causes major physiological changes in the brain, pretty much anything is fair game, even conditions that are thought to be genetic.
It would also probably force your body to consume enormous amounts of energy; our relatively slow "clock speed" is very efficient, which is why it's so successful, but operating 10x faster could very well require 10x as many calories (Wired had the protagonist tearing through boxes of donuts after coming down). This could lead to short-term hyperglycemia and long-term diseases like diabetes or even cancer.
There are lots of potentially serious side effects. As far as things like becoming a workaholic or becoming bored with people around you - I don't buy it. The massive caloric intake required to support it, and the fatigue associated with increased neural activity, would probably require more sleep, not less. It's not an amphetamine. There's also this thing called the hedonic treadmill, the theory (backed by quite a lot of evidence) that no matter what happens in our lives, we tend to return to a sort of happiness equilibrium. This works both ways, of course; it means that taking this pill probably would not, in the long term, make you any happier, no matter what you're able to accomplish; although it could make you a lot unhappier if its effects are temporary and you run out. Then you're essentially just a drug addict.