Trainer Philip Fenton will be allowed to have runners, including leading Betfred Cheltenham Gold Cup hope Last Instalment, at the Cheltenham Festival next week.
A statement read from the British Horseracing Authority said the horses Dunguib, Last Instalment and Value At Risk would be cleared for Cheltenham "on the basis of the evidence gathered and the legal advice obtained by BHA."
"After a process of gathering all available information, which included testing of the horses with Cheltenham entries, an interview with the trainer, liaison with the Irish Turf Club, and analysis of the location and testing histories of the horses, BHA has found no evidence that any of the horses in question have been administered with any substances which would be considered prohibited for an in-training test.
BHA chief executive Paul Bittar said: "Our objective upon hearing about the charges faced by Philip Fenton was to maintain the integrity of, and ensure public confidence in, the relevant races at the Cheltenham Festival.
"Hence, the priority was to obtain all available information to inform our decision as to whether there was a justified and justifiable concern that any of the horses trained by Fenton had been administered with anabolic steroids.
"The findings of this investigation have not given us a reason to believe that any of the Fenton-trained horses entered for Cheltenham have been administered with performance-enhancing substances. Therefore there was no basis, legal or otherwise, on which to prevent the horses from running.
"Our investigation included testing of the horses with entries for Cheltenham, using both blood and hair screening methods. This testing was fast-tracked at HFL Sport Science, Newmarket, and the tests showed no presence of anabolic steroids or anything else untoward.
"These facts were further supported by the individual circumstances surrounding each horse, including their training and testing histories, as well as the interview which took place between members of our Integrity team and Fenton."
The Gigginstown House Stud-owned Last Instalment has a history of leg problems, and connections have stressed the Irish Hennessy hero must have suitable ground conditions to take his chance in the blue riband.
The ground at Cheltenham was officially reported as soft, good to soft on Wednesday afternoon, and Gigginstown's racing manager Eddie O'Leary said: "This horse will not run unless the ground is soft. There is a bit of rain forecast next week and we're hoping it materialises."