Please note the current NHA Rule:

Prohibited substances in horses Rule 73.4.2 

Natural or herbal substances or remedies and/or drugs which have any of the following properties: 

73.4.2.1   antipyretic, analgesic and anti-inflammatory properties.

Cannabidiol (CBD) and Cannabidiolic acid (CBDA) are natural substances found in many Cannabis plant species, including cannabis (dagga) and hemp plants. Medicinal oils, ointment and creams which originate from these plants could contain elevated levels of these substances. Furthermore, oil preparations of pure CBD which have been of isolated from plants are now available.

CBD and CBDA are reported to have anti-inflammatory properties and these are prohibited substances in horseracing. 

It is cautioned that the use of such preparations and the use of horse bedding which has hemp plant as a component (which horses may be able to ingest) could result in prohibited substance positive findings in horses.