The B blood sample from Olympic horse Waterford Crystal has tested positive for traces of two prohibited substances, it has been confirmed.
In a statement this evening the Irish Olympic gold medallist Cian O'Connor said that minute traces of Fluphenazine and Zuclopenthixol had been found in the sample.
These are drugs more traditionally used for the treatment of psychosis in humans.
The blood sample was sent to the USA Equestrian Drug Testing and Research Laboratory in New York for testing after a sample of the horse's urine tested positive for the same substances.
Mr O'Connor said that he had always maintained that the B sample analysis would confirm that his horse was given medication by his vet, Dr James Sheeran, during therapy well in advance of the Games.
He said preliminary readings suggested a figure of 120 picograms of Fluphenazine which amounts to 0.00012 millionth of a gram in one millilitre of blood.
Mr O'Connor said the of concentration of Zuclopenthixol amounts to 0.0005 millionth of a gram in one millilitre of blood.
According to his statement, fluphenazine, traces of which was also found in another Mr O'Connor horse ABC Landliebe, "was given in the best interests of the horse at a time of rest, remote from competition, to prevent the animal re-injuring herself".
"I want to reiterate that no treatment has been deliberately given to my horses, that would enhance their performance."
Mr O'Connor said the issue was now one for the International Equestrian Federation (FEI). "I believe that I must now furnish the Federation with an explanation as to how these findings have come about.
"This explanation will be the same as that which I have always maintained and I again now reiterate to you that I in no way tried to affect the results of the Olympic Games through drugs and I am pleased that these findings have now finally and scientifically vindicated this position."
In an addendum to the statement, Dr Sheeran said that while Waterford Crystal was in full fitness, the animal needed treatment in a hydrotherapy unit for one week. "This entails standing in an enclosed space and I did not want him to injure himself."
"I chose these drugs because I wanted a calming effect without making him sleepy or unsteady on his feet, as equine medicines would. Also by this one-off injection it did not require administration by injection on a daily basis, which I chose in the best interests of the horse."
According to Dr Sheeran the result "of the B sample proves that the concentration is at a sub-therapeutic level, and would therefore have no positive effect on performance at the time of the Games".
President of the Equestrian Federation of Ireland (EFI), Ms Avril Doyle said tonight the result represented a major disappointment for the Federation and the gold medal has been "tarnished".
Ms Doyle said she was surprised that any vet would administer human anti-psychotic drugs to a horse, saying the substances "would not be the normal drugs of choice to sedate a horse either during veterinary treatment or in relation to travel".
She refused to be drawn on whether she thought Mr O'Connor was now likely to loose his gold medal, saying that due process must be allowed run its course and that it was a matter for the international federation.
The Minister for Arts, Sport and Tourism, Mr John O'Donoghue, TD also described the result as a disappointment.
Mr O'Donoghue said: "It is regrettable that the full facts of this matter were not disclosed to the Irish public at a much earlier stage, which would have been in the interests of the sport and everybody concerned."