Luke Griffith has been banned for four years after the trainer and three of his horses returned positive tests to methamphetamine.

Racing NSW stewards concluded an inquiry into the matter at Scone on Thursday when they found Griffith guilty of administering a prohibited substance to a trio of his gallopers in January and February this year.

Another Halo and How Will I Know tested positive to methamphetamine, a central nervous stimulant commonly known as ice, before winning their respective races at Tamworth on January 18.

Incensual had a positive swab to the same substance before it won at Taree on February 3.

Stewards found Griffith did not deliberately treat the horses with the illegal drug, but said the fact they won races with it in their systems was an aggravating factor in the case.

All three have been disqualified from their wins.

Griffith was stood down from handling horses following a stewards inquiry into the matter at Randwick on Anzac Day.

The trainer had provided officials with urine samples at Tamworth races in March and April and both times the results were positive to banned substances including methamphetamine.

His staff were also tested and while one stablehand returned a positive to cannabis, they were all negative to ice.

It was the fourth time Griffith had breached the rule governing banned substances in the past 15 years.

His four year penalty includes three years for administering a prohibited substance to his horses and a further year for his two personal drug tests, although four months of that will be suspended if he has professional counselling.

Griffith's ban will start on May 8 giving him seven days to maintain the care of his horses and find them new trainers.

He is not allowed to start them in races or barrier trials, including at Muswellbrook on Friday where he had accepted with eight runners.

Griffith, who has a right of appeal against the stewards' decision, can reapply for a trainers' license on January 8, 2019 if he can show he has successfully undergone counselling.