Racing officials will take another step in the battle to counteract illegal substances in horses with a revision of the rule regarding unregistered products.

Trainers will be on notice that from August 1, compounded substances can only be used if prescribed by a veterinary practitioner for use on a particular horse for a particular condition.

During the ongoing investigation into cobalt and caffeine found in Gosford Cup winner Midsummer Sun, trainer Sam Kavanagh told stewards he ordered some other products found in his stable over the internet.

Racing Australia chief executive Peter McGauran said the strengthening of the rule was to ensure the prescription and use of compounded substances was controlled and registered with the Australian Pesticides and Veterinary Medicines Authority or on the Australian Register of Therapeutic Goods.

"The requirement that all active ingredients be registered in Australia is designed to ensure that horses are not treated with compounded substances which contain active ingredients which are not registered in Australia, but may be in other jurisdictions without Australia's rigorous controls and standards," McGauran said.

McGauran said authorities were undertaking a complete re-write of the Australian Rules of Racing which should be completed by early next year.

"This will bring the rules into the modern era with plain English expression and a new structure and layout for easier reference by licensed persons," he said.

"However, there is not a scintilla of an excuse for a trainer not knowing his or her obligations under the rules.

"New or amended rules are communicated to trainers in various ways, not least of all directly through the Australian Trainers Association and NSW Trainers Association.

"Pleading ignorance of any rule, let alone those covering prohibited substances, would really have to be the last throw of the dice by a desperate individual."