Tony Martin has failed in his bid to have his three-month suspension judicially reviewed by the High Court.
The Co Meath trainer originally received a suspended six-month ban last December for a third breach of the anti-doping rules in four years. He was also fined €10,000.
That verdict from the Referrals Committee was appealed both by Martin and the Irish Horseracing Regulatory Board, who had brought the case against the trainer.
The Appeals Committee heard the case at the end of March and decided to uphold the six-month ban, but with only three months suspended. The fine was unchanged and Martin's ban was due to start this week.
However, Martin applied to the High Court for leave to judicially review the decision of the Appeals Body and an interim stay on the sanction imposed until that review took place.
The trainer's application was heard by Mr Justice Mulcahy on Tuesday and on Thursday morning he delivered the decision that Martin's application was refused on all grounds.
A statement from the IHRB confirmed: "Mr Martin's suspension commences today and all horses declared by Mr Martin have been withdrawn by order of the Stewards."
It's understood that no application has yet been lodged by any other licensed individual to train from Martin's premises for the duration of the suspension, though that remains an option.