The 27-year-old had declared using the banned substance Dehydroepiandrosterone (DHEA) before routine testing in 2025, believing it was allowed, but has been banned by an Independent Doping Tribunal Panel.
It was prescribed to Ntlabakanye by a specialist and "taken with the approval and the supervision of a medical doctor specifically appointed to manage the medical affairs of professional rugby players," South African Rugby said in a statement last year.
The Lions confirmed the ban, pending an appeal, came into force from May 13 this year.
"Lions Rugby Company confirms that it has received communication from the South African Institute for Drug-Free Sport (SAIDS) regarding the decision to sanction Lions prop Asenathi Ntlabakanye for a period of 18 months following an anti-doping rule violation," a Lions statement said.
"The Lions Rugby Company, together with MyPlayers, The Rugby Players’ Organisation, will deliberate on the appropriate next steps. During this time, the Lions Rugby Company will continue to support Ntlabakanye as he navigates the process ahead.
"No further comment will be made by the Lions Rugby Company or the player until the process regarding the way forward has been concluded."
Ntlabakanye, SAIDS, World Rugby and the World Anti-Doping Agency (WADA) have 21 days within which to file an appeal.
Ntlabakanye continued to play on while the investigation was ongoing and featured for the Lions against Leinster in the United Rugby Championship this past weekend.
He has three caps for the Springboks and would have been in the conversation for a place in the squad at next year’s World Cup in Australia.
