"This could potentially reduce the severity of symptoms or prevent the disorder from developing altogether.”
Ressi is now getting better with positive reinforcement training.
More than half of participants lost their PTSD diagnosis at the end of treatment.
The findings will offer new ideas to help those suffering from mental health problems.
Study author said: "Newer psychedelic drugs seem to be the stand-out candidates in this treatment."
In recent years there has been a surge in research for PTSD treatment.
Sufferers have noted feeling calmer, more confident and less depressed and agitated with the help of the canines.
Owls Oscar and Louie help him cope and the birds accompany him to coffee shops, restaurants - and even on trips to the supermarket.
The findings are based on over a quarter of a million US army veterans.
The condition is notoriously difficult to cure.