You should assume that any medication or supplement (including herbal substances) that has, or claims to have, an effect on horses (or any other species) is prohibited unless you have specific advice from the BHA Equine Health and Welfare Department that states otherwise.
Guidance on prohibited substances
Detection times and withdrawal periods
The difference between a Detection Time and a Withdrawal Period should be understood, as the two are different. To decide a Withdrawal Period, an adequate safety margin should be added to a Detection Time. This safety margin should be chosen by the treating veterinary surgeon, using their professional judgement, and should take into account potential biological, pharmaceutical and pharmacological variation. This clearly makes a discussion between a Trainer and their veterinary surgeon essential when considering administration of any medication which is a Prohibited Substance on Raceday.