The Horseracing Integrity and Safety Authority (HISA) and its Horseracing Integrity & Welfare Unit (HIWU) have proposed adopting a minimum reporting level (MRL) of 4.0 nanograms per milliliter in blood for the banned substance metformin in racehorses. This recommendation follows scientific research led by Dr. Heather Knych at UC Davis, which clarified metformin’s pharmacokinetics and detection times, showing that this MRL effectively distinguishes intentional administration from inadvertent exposure. The new MRL aims to standardize testing and enforcement, replacing previous inconsistent detection thresholds across laboratories and states, and will focus confirmatory testing on blood samples due to erratic urine elimination patterns.

Metformin remains prohibited with no valid veterinary use in racehorses, and violations carry penalties including suspensions, fines, and disqualification. Nine unresolved cases involving metformin are currently stayed pending Federal Trade Commission approval of the new MRL. HISA and HIWU emphasize the importance of scientific evidence in regulatory decisions to ensure fairness, safety, and integrity in horseracing, while encouraging trainers to maintain strict stable hygiene to avoid accidental contamination.