Incidentally, it is important to be aware that modern physics considers momentum and energy to be parts of a single whole. Just as the 3 dimensions of space together with time make up a 4-dimensional spacetime, the 3 components of momentum together with energy make up a 4-dimensional momentum-energy tensor. Thus, conservation of momentum and energy are not separate laws. Conservation of momentum-energy is one law—represented by a single equation in 4-dimensional spacetime. The latest experiments have verified this law to within one part out of 10 15 .
The genotype variation specifically refers to the Rs4680 SNP , which is one of the SNPs that services like 23andMe test for. So someone could sign up for 23andMe testing and only start buying modafinil if the results are favorable; considering that 23andMe sometimes holds sales at $100 or $200 and that one could easily spend this much on a single order of modafinil, testing first may not be a bad idea. But on the other hand: anecdotes are hard to come by of people who have used modafinil, been genotyped, and checked that SNP, yet I have been told by 2 Val/Val users that sublingual Modalert/Waklert did nothing for them (personal communication; 2 ) and by 4 Met/Met users that modafinil worked for them and there are 2 further anecdotes on Hacker News & Reddit ( 1 , 2 , multiple ). Besides the dubiousness of such a large effect size from a single SNP, candidate-gene results frequently disappear ( Ioannidis et al 2011 ), like what happened when 12 highly cited IQ-related SNPs failed to replicate in a well-powered 2011 GWAS and subsequent GWASes (replication being the coin of science ). As of 23 May 2013, there do not seem to have been any followup citing studies of this SNP association. Given the weakness of the evidence, one would probably have to be on the razor’s edge of deciding to try or not try modafinil before your result would make the difference.