Psychiatric service dogs affect cortisol in military veterans with PTSD

By Kerri E. Rodriguez

Up to 23% of post-9/11 military veterans in the United States have PTSD (Fulton et al., 2015), and an average of 20 veterans commit suicide each day. Many veterans are turning to specially trained PTSD service dogs to help alleviate the daily challenges that they face from the trauma of combat and war. Our latest study (Rodriguez et al., 2018) suggests that having a PTSD service dog may not only be psychologically beneficial for military veterans, but may also affect the body’s stress response system as well.

PTSD Service Dogs

A service dog is a type of assistance animal that is trained to do work or perform tasks to help a handler with a physical disability or mental condition (Americans With Disabilities Act of 1990). While some service dogs may turn on and off lights or alert to low blood sugar, psychiatric service dogs can be trained to perform tasks relevant to PTSD. For example, a PTSD service dog may learn to wake their handler up from a nightmare or distract them from anxiety experienced during a flashback.


Retired Army veteran Carlos Cruz and Hanna, his PTSD service dog from K9s For Warriors Credit:

Research from both our research group (O’Haire & Rodriguez, 2018) and others (Yarborough et al. 2017; Klopp, Hunter & Kreuz, 2017; Bergen-Cico et al., 2018) has found that psychiatric service dogs can have positive effects on mental health, social functioning, and quality of life among military veterans with PTSD. However, these findings are self-reported; while veterans’ perceived stress levels may be lower when their service dog is present, we can’t account for the possibility that these reports may be inflated, or biased.

In our most recent study (Rodriguez et al., 2018), we sought to test the hypothesis that a PTSD service dog would have an effect on the stress hormone cortisol – a physiological biomarker that can’t be inflated or biased.

This research is important, as without empirical studies that establish the therapeutic efficacy of PTSD service dogs, this popular practice used by thousands of military veterans across the US will continue to be empirically unsupported. The U.S. Department of Veterans Affairs (VA) has stated that they will not fund psychiatric service dogs as a treatment for PTSD as there remains a lack of researchon their psychological and physiological effects. While we have preliminary qualitative and quantitative evidence that service dogs may be helping veterans with PTSD in clinically meaningful ways (Krause-Parello, Sarni & Padden, 2016) the field needs rigorous, replicable science behind these reports.

PTSD and Cortisol

Cortisol is famously referred to as “the stress hormone” – this is because cortisol is a main product of the brain’s stress response system. Every morning when you wake up, you experience a 50-75% increase in the levels of circulating cortisol in your bloodstream (Pressier et al., 1997). In healthy adults, the magnitude of this cortisol awakening response, or the CAR, is continuously linked to both higher acute and chronic stress (Chida & Steptoe, 2009).

However, research suggests that individuals with PTSD have abnormally low production of cortisol in the mornings (Wessa et al., 2006). Because of this deficiency in cortisol production, a higher CAR may not actually mean more stress in this population. In fact, highermorning cortisol may indicate that an individual with PTSD is exhibiting a cortisol profile closer to that of healthy adults without PTSD symptoms.

PTSD Service Dogs and the CAR

Our recent research (Rodriguez et al., 2018), published in Psychoneuroendocrinology, aimed to compare the cortisol awakening response among a group of military veterans with PTSD who either had a service dog or were on the waitlist to receive one.

To conduct the study, we teamed up with national service dog provider K9s For Warriors, one of the largest providers of PTSD service dogs in the country. We had 73 veterans participate in the study, including 45 who had already been placed with a service dog and 28 on the waitlist.

To measure the CAR, veterans simply had to fill up two vials: one immediately after waking up, and the second about 30 minutes later. By using user-friendly instructions, color-coded vials, and text messaging to remind participants when to collect their samples, we collected hundreds of samples from veterans across


Instructions given to participants on how to collect saliva samples. Credit: Kerri Rodriguez

the country. We also asked veterans to fill out an online survey, which asked about their demographics, sleep, and psychosocial health.

What Did We Find?

 We found that having a service dog was indeed related to having higher cortisol production in the morning. Specifically, after controlling for several demographic and medical characteristics that may influence cortisol, we found that having a service dog was significantly associated with a larger CAR.


A graphic display of the cortisol awakening response (CAR) and the area under the curve with respect to increase (AUCi) by group. Note: Covariate-adjusted CAR and AUCi are displayed as least square means (LSM) from mixed model output, controlling for age, sex, use of a mobility aid, body mass index (BMI), physical health (VR-12 PCS), alcohol use, sleep disturbance, cortisol-influencing medication, waking cortisol value, and wake time.

Although we don’t know if this magnitude difference in the CAR is clinically relevant for PTSD, a higher CAR among those with a service dog may suggest better health and wellbeing in this population.

We also found that those with a service dog reported significantly less PTSD severity as well as less anger, anxiety, sleep disturbance, and alcohol abuse symptoms than those on the waitlist. These findings mirror that of similar studies that have found evidence for the therapeutic efficacy of service dogs for military veterans with PTSD (Krause-Parello, Sarni & Padden, 2016).

While this finding is important, it should be interpreted cautiously. As this study was cross-sectional, we can’t determine that the findings are causational. That is, we still don’t know if a PTSD service dog directly affects cortisol production in this population. We also don’t have a complete grasp of the mechanism for how dogs can influence the body’s stress response system, nor do we know how individual differences in either veterans or service dogs might be important for understanding our findings.

The next step to answer these questions is already underway. Our research group is currently conductinga large-scale National Institutes of Health (NIH) funded clinical trialin which we will be teaming up with K9s For Warriorsto follow veterans with and without service dogs over an extended period of time. This will allow us to be able to look at within-individual cortisol levels both before and after getting a service dog to see how these changes may occur over time on a much larger scale.


  1. Fulton, J.J., et al., The prevalence of posttraumatic stress disorder in Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) Veterans: a meta-analysis.Journal of anxiety disorders, 2015. 31: p. 98-107.
  2. Rodriguez, K.E., et al., The effect of a service dog on salivary cortisol awakening response in a military population with posttraumatic stress disorder (PTSD).Psychoneuroendocrinology, 2018. 98: p. 202-210.
  3. Americans With Disabilities Act of 1990, Pub. L. No. 101-336, 104 Stat. 328. 1990.
  4. O’Haire, M.E. and K.E. Rodriguez, Preliminary efficacy of service dogs as a complementary treatment for posttraumatic stress disorder in military members and veterans.Journal of consulting and clinical psychology, 2018. 86(2): p. 179-188.
  5. Yarborough, B.J.H., et al., An Observational Study of Service Dogs for Veterans With Posttraumatic Stress Disorder.Psychiatric Services, 2017. 68(7): p. 730-734.
  6. Kloep, M.L., R.H. Hunter, and S.J. Kertz, Examining the Effects of a Novel Training Program and Use of Psychiatric Service Dogs for Military-Related PTSD and Associated Symptoms.Am J Orthopsychiatry, 2017. 87(4): p. 425.
  7. Bergen-Cico, D., et al., Dog Ownership and Training Reduces Post-Traumatic Stress Symptoms and Increases Self-Compassion Among Veterans: Results of a Longitudinal Control Study.The Journal of Alternative and Complementary Medicine, 2018. 24(12): p. 1166-1175.
  8. Krause-Parello, C.A., S. Sarni, and E. Padden, Military veterans and canine assistance for post-traumatic stress disorder: A narrative review of the literature.Nurse Education Today, 2016. 47: p. 43-50.
  9. Pruessner, J., et al., Free cortisol levels after awakening: a reliable biological marker for the assessment of adrenocortical activity.Life sciences, 1997. 61(26): p. 2539-2549.
  10. Chida, Y. and A. Steptoe, Cortisol awakening response and psychosocial factors: A systematic review and meta-analysis.Biological Psychology, 2009. 80(3): p. 265-278.
  11. Wessa, M., et al., Altered cortisol awakening response in posttraumatic stress disorder.Psychoneuroendocrinology, 2006. 31(2): p. 209-215.

Citation:Rodriguez, K. E., Bryce, C. I., Granger, D. A., & O’Haire, M. E. (2018). The effect of a service dog on salivary cortisol awakening response in a military population with posttraumatic stress disorder (PTSD). Psychoneuroendocrinology, 98, 202-210.

About the Author: Kerri Rodriguez is a 4thyear Ph.D. student of Dr. Marguerite O’Haire in the Center for the Human-Animal Bond at Purdue University. Her research focuses on studying the psychological and physiological effects of service dogs both within military veterans with PTSD as well as individuals with physical disabilities. You can reach her via emailor linkedin. To learn more about the Center for the Human-Animal Bond’s research, visit their website at

The ISAZ Student Blog is posted quarterly  and each post is authored by a different student member of the International Society for Anthrozoology. Interested in authoring a post? Please see our submissions page for details on how to apply. 

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