Gerald Butler, a trainer based in Illinois for most of his 33-year career, has been provisionally suspended by the Horseracing Integrity and Welfare Unit on charges of possession of levothyroxine, a banned substance that stimulates thyroid function, according to a HIWU ruling. Butler, who has won 512 races with purse earnings of $3.6 million since he began training in 1991, was stabled at FanDuel Sportsbook and Horse Racing in East St. Louis, Ill., at the time the suspension was announced. He also was charged with “two acts of retaliation and threats/intimidation,” according to HIWU. Possession of a banned substance like levothyroxine carries a recommended penalty of a two-year suspension. Levothyroxine can have a number of impacts on a horse biologically, since the thyroid gland regulates a variety of functions, including appetite, metabolism, and oxygen consumption. :: Get the Inside Track with the FREE DRF Morning Line Email Newsletter. Subscribe now.  Regulators began cracking down on products containing synthetic thyroxine a decade ago after several studies revealed that a large number of horses were receiving regular administrations of the drug without a diagnosis of thyroid dysfunction.  HIWU has prosecuted four cases of levothyroxine possession and has five other cases pending since the company launched the enforcement arm of the Horseracing Integrity and Safety Authority’s drug-testing program in May of last year.  Butler had won 20 races from 83 starts this year before the suspension was issued, for a strike rate of 24 percent. Last year, he won 29 races from 116 starts, for 25 percent. His lifetime win rate is 15 percent, but in eight of the past 11 years, his win rate has exceeded 20 percent, hitting 26 percent in 2017 and 27 percent in 2019. :: Want to learn more about handicapping and wagering? Check out DRF's Handicapping 101 and Wagering 101 pages.