Physiology of human-horse interactions during substance withdrawal within psychotherapy participants

Psychotherapy incorporating equine interaction (PIE) is emerging as an effective treatment for substance use disorder (SUD); however, research concerning physiological impacts of PIE during substance withdrawal is lacking. This study investigated impacts of PIE on salivary cortisol concentrations and heart rates in SUD patients during withdrawal. Heart rate and cortisol concentrations were also measured in horses to investigate potential human-horse coupling during PIE. Saliva samples and heart rates were collected from SUD patients (n = 18) and their therapy horses (n = 4) prior to the introduction of the horse and following equine interaction within a residential psychotherapy program during the substance withdrawal period. Without the presence of the horse, the equine environment during the first week of withdrawal produced lower () cortisol and heart rate measures than found in the equine interaction for the SUD patients. Human heart rates, however, decreased () in the second week in response to the equine interaction. A strong negative correlation (r = −0.9, ) was found within the changes in human and horse cortisol concentrations during week two as human cortisol concentrations decreased while horse cortisol concentrations increased. Results indicate equine interaction during psychotherapy is more effective in the second week than the first at mitigating stress for withdrawing residential SUD treatment program patients and the equid environment, even without the presence of a horse, can positively impact stress parameters in withdrawing SUD patients during the first week of treatment.