Objective: Stress and its sequelae are very common in adults with autism spectrum disorder (ASD) without an intellectual disability (ID). Animal-assisted therapy (AAT) has shown physiological stress-reductive effects in children with ASD. The aim of the current study was to examine the acute psychophysiological response to an AAT session, and to examine the longer-term stress-physiological effects of the intervention, up until 10 weeks post-treatment, in comparison to waiting-list controls.

Method: A randomized controlled trial with pre-intervention (T0), post-intervention (T1: 10 weeks) and follow-up (T2: 20 weeks) measurements of neuroendocrine and cardiovascular measures, was conducted in 53 adults with ASD (N = 27 in intervention arm; N = 26 in control arm). Within the intervention group, stress-physiological data were collected during the 5th therapy session (acute effects). Data were analyzed with mixed models for outcome measures cortisol, alpha-amylase, heart rate variability and sympathetic activity.

Results: The AAT interventional session was significantly associated with reduced cortisol levels (β = -0.41, p = .010), while parasympathetic and sympathetic cardiovascular activity remained unaltered. No significant changes were found for stress-physiological measures at post-treatment time points.

Conclusions: Acute stress reduction, reflected in significant reduction in cortisol levels, was found during an AAT session in adults with ASD, without ID. More research is needed to explore to what extent the specific factors of AAT have contributed to the decrease in cortisol and whether stress reduction is possible for the longer-term.