Suspended trainer Mahmood Al Zarooni was guilty of a "widespread systematic misuse of illegal substances", according to the British Horseracing Authority.
Newmarket-based Al Zarooni was banned for eight years last Thursday after he admitted administering anabolic steroids to 15 horses in his care.
The BHA confirmed the 37-year-old trainer, who was at the helm of the Godolphin-owned Moulton Paddocks, had personally brought the drugs into the United Kingdom on a flight from Dubai, where horses in training can be given anabolic steroids and can race 28 days later.
His assertion he did not know that such administration was not permitted in the United Kingdom was considered "untruthful" by the BHA, who on Tuesday published its reasons for suspending Al Zarooni for eight years.
"The (disciplinary) panel takes a very dim view of the sheer volume of horses who were subjected to these unlawful medication regimes," read a BHA statement.
"This was a widespread systematic misuse of illegal substances which are absolutely prohibited under the rules.
"Nearly a quarter of the 45 horses tested at the stables had positive samples.
"These were horses in training, some of which were entered into races in April and May.
"The panel considered there was no excuse for Al Zarooni to be in any doubt as to the illegality of administering anabolic steroids.
"The BHA has publicised this issue and following the case of Howard Johnson in 2011 (who was suspended one year for using steroids on two horses), the matter was given further prominence.
"Al Zarooni's assertion at the hearing that he did not know that such administration was not permitted in the UK was simply not truthful."
Al Zarooni was officially charged with rule breaches related to prohibited substances, duty to keep medication records, and conduct prejudicial to racing.
The case, widely regarded to be the most serious doping scandal in recent British racing history, led to Godolphin principal Sheikh Mohammed, who was "appalled and angered" by Al Zarooni's actions, locking down Moulton Paddocks.
The BHA said Al Zarooni had the resources at Moulton Paddocks to seek credible advice from the stable's vets, and that his "attempt at cheating" was only uncovered following a BHA-led 'testing in training' visit to his yard on April 9.
"He asserted that he was only trying to do the best for his horses who were unwell," said the BHA.
"He did not have a credible explanation as to why he had not discussed the matter with the stable's veterinary surgeons or entered a record of the administration of the drugs in the stable's medication books.
"The panel concluded that Al Zarooni sought to confer an unfair advantage on his horses by the underhand administration of illegal medication.
"His attempt at cheating was uncovered by the regulatory inspection and he had no justifiable excuse for his behaviour.
"He had access to expert veterinary advice from a number of sources but he deliberately ignored this resource and chose to covertly administer to horses in training anabolic steroids which he had brought back into the UK in his luggage from Dubai.
"There was no reason for Al Zarooni's failure to inform the veterinary surgeons of this treatment intervention unless, as in this case, the substance that was being administered was prohibited.
"The panel is firmly of the view that this was not an accidental or inadvertent misunderstanding of the rules - this was a deliberate flouting of the governance framework of British racing by one of the most high-profile Flat trainers working in the racing industry."