The more that a fighter trains the moire nerves affect them.
If a fighter has in=vested months of their lives in the fight and sacrificed all his comforts, he becomes extremely nervy before the fight.

From my limited knowledge of the drug it does efect the user in all the ways you have mentioned, however as I mentioned, if taken at correct times it could be used for this purpose. It may not be ideal, but I can envisage an athlete with poor guidance using the drug to calm nerves before a fight.

As your story suggested any foreign substance alters the body and pretty much negates training that has been done, but if a fighter were to kill the nerves, by whatever means in the hours coming up to the fight and was given back his "senses" before the figjht it would be an excelent method.

Drugs aren't uncommon in boxing, so many boxers take cocaine for confidence once their careers end.