Racehorse trainer Mahmood Al Zarooni has been disqualified for eight years after 11 of his horses tested positive for anabolic steroids, the British Horseracing Authority (BHA) confirmed.
The 37-year-old was given the punishment after a disciplinary hearing at the BHA headquarters in central London on Thursday afternoon.
The BHA made the announcement on social media, tweeting: "Mahmood Al Zarooni has been disqualified for eight years following today's Disciplinary Panel hearing."
The scandal has already caused Al Zarooni's stables to be locked down by renowned owner Sheikh Mohammed, saying he was "appalled and angered" by events.
Al Zarooni was charged with rule breaches related to prohibited substances, duty to keep medication records, and conduct prejudicial to racing.
He admitted wrongdoing ahead of Thursday's hearing, in which he was not being legally represented, saying he had made a "catastrophic error".
Speaking on Monday, he said he did not realise he had broken any rules as the horses were not racing at the time.
Samples were taken earlier this month from 45 horses trained by Al Zarooni at Moulton Paddocks Stables, Newmarket.
Subsequent analysis showed 11 of the samples contained ethylestranol and stanozolol, which are prohibited substances.
In a written statement after the hearing, Al Zarooni reiterated his regret over the issue.
He said: "First and foremost, I would like to apologise to his Highness, Sheikh Mohammed, as well as all those involved in Godolphin and the public.
"I accept it was my responsibility to be aware of the rules regarding prohibited substances in Britain.
"I can only apologise. I have made a catastrophic error."
Simon Crisford, on behalf of Godolphin, described it as "a terrible day for British racing".
He added: "This is a terrible situation. It's an awful situation that Godolphin has found themselves in.
"Mr Al Zarooni acted with awful recklessness and caused tremendous damage, not only to Godolphin and British racing.
"I think it will take a very long time for Godolphin to regain the trust of the British public.
"We're shocked and completely outraged by the actions he has taken."
Crisford also confirmed Al Zarooni had mentioned the names of three other people - two foremen and a veterinary assistant, all Asian - who were "involved". However, he said the assistant had not broken any rules because he was unaware what substance he was administering.
Crisford said Al Zarooni had previously administered steroids in Dubai, where it is not prohibited.
Referring to the contravention of British rules, he added: "This is an isolated incident at the hands of a reckless person who has shown no respect for horse racing in this country."
Asked about Sheikh Mohammed's views on the incident in Britain, Crisford said: "He will want, first and foremost, to see this put behind us. He will want to make sure this mistake never happens again."
BHA chief executive Paul Bittar said the punishment would reassure the public and the horse racing industry that the use of performance-enhancing drugs would not be tolerated.
In a statement, he said: "The relevant rules in this case are explicit in that the use of anabolic steroids in horses in the care of a licensed trainer is prohibited and that strict liability for everything administered to horses while they are in training lies with the trainer.
"We believe that the eight-year disqualification issued to Mahmood Al Zarooni by the disciplinary panel, together with the six-month racing restriction placed on the horses in question by the BHA, will serve to reassure the public, and the sport's participants, that use of performance-enhancing substances in British racing will not be tolerated and that the sport has in place a robust and effective anti-doping and medication control programme."
The BHA's investigation has established that the substances in question were administered on the instruction of Mahmood Al Zarooni.
He said the full details of how the substances were administered - on the instruction of Mr Al Zarooni - would be published later.