Substance withdrawal during psychotherapy incorporating equines: A preliminary investigation of the role of neurotransmitters during treatment. Substance withdrawal presents a barrier to substance use disorder (SUD) recovery in part due to symptoms implicating neurotransmitters and their metabolites. Despite this relationship, research investigating alternative treatments such as psychotherapy incorporating equines (PIE) have primarily targeted vital signs and cortisol concentrations. Previous research has also proposed benefits of human-horse physiological coupling, but the role of neurotransmitters in the relationship between humans and horses during PIE has not yet been investigated. The purpose of this study was to characterize ne...