The Ray Walker case is the first in Ireland to feature the banned substance meldonium.
The footballer, who returned to the Carlow squad in November after a long absence, tested positive for meldonium in February. He maintains he did not knowingly take the banned substance but has accepted the maximum four-year ban.
Primarily used as a heart medication, meldonium increases the flow of blood and oxygen throughout the body. Maria Sharapova was banned after a positive test for meldonium in 2016.
"It's not a substance that we have detected in a sample previous to this," Dr Una May, head of Sport Ireland's anti-doping unit, told RTÉ Sport.
"It's quite common in some parts of the world, it's not as common here.
We would consider it unusual in that it's not available in any Irish medications and it's not for sale in Ireland.
"It was unusual and we were surprised to see it but we can't speculate as to how it got there or how common it is or how available it is."
Sharapova's two-year ban was reduced to 15 months on appeal. Walker, a joint-statement issued earlier today by the GAA and Sport Ireland noted, had accepted the imposition of an automatic four-year ban and waived his right to a hearing on April 1. Following receipt of the 'reasoned decision' outlining the facts of the case, including a statement of his right to appeal, Walker filed an appeal and sought a reduced ban on April 21.
Walker then issued a statement to the media on Tuesday stating he had decided to accept the ban, before confirming to Sport Ireland on Wednesday he had withdrawn his appeal.
The GAA has since defended its anti-doping education programme after Walker, who says he didn't receive any such training, failed the test.
The Association says that 2,200 players involved in county panels this year have completed their anti-doping education programme, including 36 players on the Carlow football panel. It is mandatory for players to complete the programme by March 31 each year to receive Government grants.
The GAA noted this is the fourth time an inter-county player has tested positive since the introduction of testing in 2001.
A separate GAA statement read: "While it is ultimately the responsibility of individual players to be aware of the provisions of the Irish Anti-Doping Rules, including items on the Prohibited List, the GAA, in conjunction with Sport Ireland, and with the support of the GPA and of backroom personnel involved with all of its inter-county teams, has established an extensive anti-doping education programme for inter-county players over the last number of years.
"The Association has trained a total of 46 anti-doping tutors and makes education available to its players through a combination of face-to-face workshops or through completion of the GAA’s online anti-doping course. In excess of 2,100 players received formal education in 2019 in this manner. To date in 2020, more than 2,200 players have completed formal education.
"In addition, completion of formal anti-doping education before March 31st annually has been a pre-requisite for participation in the Government Support Schemes for inter-county players since 2018. For the record, last year 36 players on the Carlow Football Panel completed formal anti-doping education. As of today, 36 players in the 2020 squad have also done so.
"Sport Ireland conduct well in excess of 100 tests per year on inter-county players (137 tests were carried out in 2019), both in competition and out of competition (i.e. at team training sessions). While the GAA is disappointed to note another adverse analytical finding, the Association remains committed to upholding the provisions of the Irish Anti-Doping Rules and will continue its ongoing efforts to provide education and advice to its players in this context."