Irishman Butler, based in Newmarket, England, admitted injecting horses with a product for injured joints and faced seven charges of breaching the Rules of Racing.
A BHA disciplinary panel said Butler administered the prohibited substance Rexogin which contains stanozolol - the steroid used by disgraced Olympic sprinter Ben Johnson at the 1988 Seoul Olympics - to four horses using a method restricted by law to qualified veterinary surgeons.
Butler, whose big-race wins include the 1999 Eclipse Stakes at Sandown with Compton Admiral, argued that vets had assured him the substance did not breach rules.
But the panel concluded that Butler's actions were "an appalling breach of his duty to look after the interests of the horses in his care and amounted to conduct that was seriously prejudicial to the integrity, proper conduct and good reputation of horse racing in Great Britain".
Butler is the second trainer to be banned this year by the BHA for doping horses.
Mahmood Al Zarooni, who trained for Godolphin owner and Dubai ruler Sheikh Mohammed bin Rashid al-Maktoum, was banned by the BHA for eight years after being found guilty of administering anabolic steroids at his stables in Newmarket.