Leading bookmaker Ladbrokes said on Tuesday it had refunded bets on some of the horses which tested positive for banned steroids.
Ladbrokes said it had refunded £200,000 ($305,000, 235,000 euros) of ante post stakes on horses in the care of Classic-winning Godolphin trainer Mahmood Al Zarooni following what it called "exceptional circumstances".
The horses concerned were the unbeaten filly Certify, Desert Blossom, Artigiano and Restraint of Trade.
"Certify was one of the most popular ante post horses of the season. She was the big race favourite all winter but given the circumstances we feel it's only fair customers get their money back," said Ladbrokes spokesman Alex Donohue.
William Hill also followed suit while Paddy Power said that they would refund at the very least thpose punters who had backed Certify for the 1000 Guineas, the first fillies classic of the season which is run at Newmarket at the end of next week.
Kate Miller, head of William Hill's PR team, tweeted: "Godolphin horses William Hill will refund ALL AP bets on; 1000 Guineas, Certify & Desert Blossom. 2000 Guineas; Artigiano/Restraint Of Trade."
Al Zarooni's only intended runner on Tuesday, Press Room, was taken out of a race at Yarmouth. The horse was reported to be coughing.
Godolphin, the brainchild of Dubai ruler Sheikh Mohammed al-Maktoum, said on Monday the doping scandal was a dark day for the team and it was carrying out an urgent review.
Al Zarooni - who faces a lengthy suspension from the sport - said he had made a "catastrophic error".
Godolphin was founded in 1992 and has recorded over 2,000 wins - including 200 Group One victories - in 14 countries.