Last week Godolphin trainer Mahmood Al Zarooni had his licence revoked for eight years by the BHA for doping racehorses.
Eleven horses, trained by Al Zarooni for Dubai ruler Sheikh Mohammed bin Rashid al-Maktoum, tested positive for anabolic steroids, including stanozolol. Emirati Al Zarooni also admitted administering prohibited substances to four other horses.
Gerard Butler told Monday's Independent newspaper that medication known as Sungate, a treatment for injured joints which contains stanozolol, had been given to several horses at his stables in Newmarket, southern England - the headquarters of British flat racing.
He said Sungate was recommended by his vets and that he was told it may have been prescribed to as many as 100 racehorses trained in the town.
"I have been very uncomfortable over the past few days, hearing and reading about the Al Zarooni case," Butler told the newspaper.
"I feel people need to know about what has happened in my yard. I know I'm obliged to satisfy myself that each and every treatment is within the rules, and I failed to do so in this case.
"But I am certain that this medication has been misunderstood by many others. And I just hope that the BHA is being suitably rigorous in establishing whether that is indeed the case."
The BHA said it was investigating a number of positive samples obtained from horses at Butler's yard, following a testing in training visit on February 20.
"While conscious of the need not to prejudice the outcome of the current inquiry, the investigation has established that the source of the positive samples was a veterinary product, licensed in the EU and legally imported for use by a veterinary practice, the initial administration of which was recommended by a vet," the BHA said in a statement.
"One of the objectives of this investigation is to clarify the extent to which this product has been distributed and administered to horses in training."
- Mahmood Al Zarooni
- Gerard Butler