The case revolves around a doping violation in equestrian sports involving a rider, referred to as N., and two horses, C. and L., which tested positive for hydroxydiphenhydramine, a metabolite of the prohibited substance diphenhydramine, during post-competition drug tests in October 1991. The substance, an antihistamine with sedative effects, is banned under Fédération Equestre Internationale (FEI) regulations. N. argued that the horses were treated with Benadryl and Enelbin for legitimate medical reasons—horse L. for a head injury during transport and horse C. for external curative treatment. However, the FEI’s Judicial Committee disqualified N. and the horses from both competitions, revoked prize money, imposed a four-month suspension, and ordered payment of procedural and analysis fees totaling CHF 4,250, along with public disclosure of the sanctions. N. appealed to the Court of Arbitration for Sport (CAS), which upheld the FEI’s ruling but adjusted the sanctions. The CAS emphasized the strict liability principle in anti-doping regulations, holding N. responsible for ensuring no prohibited substances were administered and for reporting any treatments to the competition veterinarian. While the tribunal acknowledged the unintentional nature of the violation, it found N. negligent for failing to verify the legality of the substances and not informing the veterinarian. The CAS deemed the laboratory analyses reliable, dismissing N.’s argument about the lack of quantitative data, as FEI rules do not require such specificity. Mitigating factors included N.’s reliance on their veterinarian, the common use of Benadryl in veterinary practice, and the lack of explicit warnings on the bottle about its prohibited status. The CAS partially upheld the appeal, overturning the FEI’s initial decision and imposing a fine of CHF 4,000 instead of a suspension. The final ruling disqualified N. and the horses from the competitions, revoked prizes, and required payment of the fine. The case underscores the importance of strict adherence to anti-doping regulations and the consequences of negligence, even in unintentional violations, while balancing fairness in enforcement. The CAS issued its final decision on September 10, 1992.