NSW trainers have been put on notice regarding the testing for two substances - mannitol and glaucine.

Racing NSW stewards issued a release on Tuesday saying the Australian Racing Forensic Laboratory had the capacity to detect the presence of both in raceday samples.

Stewards said Mannitol was considered to be a diuretic and masking agent when given by intravenous injection.

Glaucine is an alkaloid found is certain plants in the poppy variety and is also found in other plants such as the tulip poplar tree and acts on the central nervous system and would be categorised as an anti-inflammatory agent and bronchodilator among other things.

It is not contained in any legitimate or registered human or veterinary medicines or supplements available for use in Australia.

Stewards further emphasised trainers should not use any unregistered or non-APVMA compliant products, including herbal and "natural" remedies, that are claimed to be of benefit in treating or managing horses known to be bleeders.

"Such products may deliberately or inadvertently contain glaucine, and its detection would constitute the finding of a prohibited substance," they said..