A. The drugs could be too expensive for universal use.
A1. I doubt if they would be in the millionaire-only club — I don’t think any other drug is, really, not if there are a lot of customers to spread the fixed costs over.
A2. But it would be easy for them to be too expensive for general use in non-first-world countries. Them that has, gets. Even if too expensive for general use in a poor country, the kakistocrats could probably afford them, making revolution harder. Dictators would, as a perk, get smarts as well as power. The gap between us and , say, Guinea Bissau would become awesome.
A3. There might be a medium-sized but significant time lapse between elite use and general use. Would our government disintegrate in the interim?.
A4. A cabal keeps the drugs secret and strives for world domination. Sounds like fun. See E.
B. There might be side effects.
B1. You die after a while. Flowers for Algernon.
B2. You are physically messed up but don’t die, something like the kids with torsion dystonia. I doubt this though, because these mutations are very recent and have not been refined by natural selection. And most people with that torsion dystonia mutation never get sick. Since that is the case, it is probably easy to improve them, reduce side effects, etc. They are non-optimized and so can be optimized. If nothing else, take a break now and then from the drugs. Carriers can’t do that. Hmm.. if there is a risk of physical problems, would people use them anyhow? Most would-be Olympians would take a drug that killed them in five years if it gave them a gold medal: are wannabe Nobelists that tough? Would we use it in a desperate situation, a war? Should we force it on our researchers, for the greater good?
B3. The drugs change your personality in interesting and/or undesirable ways. This side effect too could probably be ameliorated, but it might be tricky.
C. They only work if taken in early life.. Then us geezers might be pushed aside by the rising generation in a new and spectacular way. In fact, the country might not even be run by middle-aged people at all.
C1. They work some, not as well, if you start late.
D. They increase intelligence a lot. Might be possible: if we’re talking the Ashkenazi mutations, hardly anyone has more than one, just about nobody more than two. One in two thousand Ashkenazi, at most, carry a Tay-Sachs mutation and a Gaucher mutation, the two most common. But using drugs, we could in principle give you the torsion dystonia effect and the Gaucher-carrier effect and the Tay-Sachs–carrier effect and the Canavan-carrier effect. and the familial dysautonomia carrier effect. As a rough guess, might give you considerably more than 20 pts — torsion dystonia gives about ten all by itself.
D1. Add even one standard deviation and society is transformed. Somehow I think that Poul Anderson”s Brainwave missed the point.
D2. Real smart people become so much smarter as to be un-understandable by usuns. This is a lot like Vinge’s Singularity, or his old short story Bookworm, Run !.
D2a. They stop having children altogether. if you extrapolate, that is certainly the trend, at least among women. The higher the IQ, the lower the fertility.
D2b. The incomprehensibly smart all convert to Catholicism. Or to something else. To them it is obvious.
D2c. The incomprehensibly smart figure out ways to get even smarter. This story can’t be told.
D3. We run similar genetic analysis on famously smart people, looking for strong IQ genes. Before we’re done we dig up Newton, Gauss, Clerk Maxwell, and steal Einstein’s brain
D4. We test it on chimps and overshoot. That could be bad.
E. The government bans it — the powers that be want to stay the powers that be. It’ll only work if the powers that be have their own trump — say, real machine intelligence, or maybe people souped-up with a computer connection, as in Starswarm. Or, hydrogen bombs, coupled with a world technological inquisiton, especially biotechnology. See Niven’s ARM stories, Poul Anderson’s Shield, [Jerry Pournelle's] CoDominium, Vinge’s The Peace War .
E1. Some countries ban it, while other countries, or other sub-national groups, try it. Beyond This Horizon, many others.
E2. Groups that currently have such genetic advantages wish to keep their edge and support the ban. Up to now, people could kill or oppress you but they couldn’t be you, couldn’t steal your essence. That was then.
E3. The government bans it for everyone other than themselves, for good national-security reasons. We wouldn’t want super-smart terrorists, would we? Shortly thereafter, hereditary rule is imposed. it now works because regression to the mean doesn’t make the nephew stupid; intelligence is a perk of office.
E4. The government only allows use on the slow: only for leveling. Never work of course.