Maybe. Perhaps a reader with access to the journal article and a willingness to work through the material can attempt to assess the study's value, but based solely on what's in the first link the conclusion is dubious.
These are the reported results: modafinil (sold as Alertec, Modavigil, and Provigil) improved players' performances by an average of 15%, while methylphenidate (sold as Ritalin) improved players' performance by 13%. Not to be missed: caffeine intake resulted in a 9% increase. (What exactly that means isn't spelled out: is it in terms of IPRs? Percentage scores in a player's results? Something else?)
Was the methodology good? Is it ethical to ingest these substances (at least those which are prescription-only) for these purposes? Is it safe? These are all important questions to be asked before anyone considers taking modafinil and/or methylphenidate for performance-enhancing purposes, and as FIDE and national chess federations decide whether or not to ban such substances and test for them.
There is an apparent problem with the study, however, and it's very odd that it is swept under the statistical rug - at least in the publicly available material. Apparently those taking either modafinil or methylphenidate played more slowly, and games lost on time were thrown out. Since tournament play always involves time controls, such an exclusion is an absurdity if the aim is to evaluate the effect on performance in competitive play.
But maybe I'm missing something; if so, I count on my savvier readers to set me straight here.