The Paul Smith-trained Ferniehirst is free to run in the $500,000 Country Championship final after an inquiry into a positive test to a human anti inflammatory medication.

A pre-race blood sample taken from the mare before she qualified with her second in the Northern Rivers heat on March 11 showed the presence of naproxen.

At an inquiry at Coffs Harbour on Thursday, Smith told Racing NSW stewards he had been taking the medication for a shoulder injury.

The blood sample showed a level of 9ng/ml but a post-race urine sample did not detect the substance.

Stewards found the most likely cause of the analyst's findings was stable contamination and that because the naproxen could not be confirmed in the urine sample, the finding did not constitute the detection of a prohibited substance under the Rules of Racing.

Smith was advised that in circumstances whereby he is taking medication that contains a prohibited substance he must ensure that he takes all reasonable precautions with his stable practices to prevent the possibility of contamination.

Ferniehirst was at $34 on Thursday with Don't Give A Damn favourite at $4 ahead of Suncraze ar $4.20.