Update, 19:58 CET: While we didn't know this originally, HGH is banned under FIFA law, as per this document: "On the 2006 FIFA list of prohibited substances, HGH belongs to category S2, 'hormone and related substances.'"
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Sky Sports' Barcelona-based writer Graham Hunter appeared on Irish radio show Off the Ball recently, and casually mentioned that Barcelona's (and Spain's--this will be important) star midfielder Xavi has used HGH (Human Growth Hormone) to deal with a calf strain. Hunter nonchalantly mentions Xavi's HGH use, then went on to explain that "was how they were treating him, very openly and publicly. [HGH] is an injection that Barcelona has been using to deal with muscle fatigue and muscle strains in their players over the past couple of years. They use it as a treatment."
Human Growth Hormone is banned in most major sports, certainly in all the major American leagues (MLB, NFL, NBA) and cycling. It's a synthetic version of the naturally occurring hormone that helps spur muscle and bone growth. In this case, Barcelona are using HGH to spur muscle regrowth and repair.
If this is true (we are inclined to believe Hunter, as he's a respected, famous journalist and has been very pro-Barcelona in the past), then there could be something really, deeply wrong with the sport generally. If doping allegations are treated so trivially, then there is really little hope of ever confronting doping on an international stage in soccer.
Oh, and just so we're clear: this is not meant to attack Barcelona. On the contrary. We're reporting this to shed a little light on the problem at large; if Xavi and Barcelona use it, there's definitely someone who uses it at Real Madrid. And at United. And everywhere else.