But not everyone recognizes the dogs as legitimate. Hernandez and Aragon have had incidents where people have questioned their bringing a dog into a public place. Hernandez even filed a lawsuit last year, alleging that he was kicked out of a fast-food restaurant because of his dog. It was later settled out of court.
The legal side
Part of the reason that psychiatric service dogs present a tricky situation is that different federal agencies implement different regulations with respect to them.
The Department of Justice, in its guidelines for implementing the Americans with Disabilities Act, defines "service animals" as "dogs that are individually trained to do work or perform tasks for people with disabilities." This can include "alerting and protecting a person who is having a seizure, reminding a person with mental illness to take prescribed medications, calming a person with Post Traumatic Stress Disorder (PTSD) during an anxiety attack, or performing other duties."
The guidelines state that dogs whose "sole function is to provide comfort or emotional support do not qualify as service animals under the ADA."
But service animals are required to be allowed in establishments that sell or prepare food, for example. And "allergies and fear of dogs are not valid reasons for denying access or refusing service to people using service animals," according to the guidelines.
In a situation such as a school classroom or a homeless shelter, the allergic person and the person with the service dog should be assigned to different locations if possible, the guidelines say.
The Department of Transportation, on the other hand, makes reference to animals that "assist persons with disabilities by providing emotional support." Its guidelines allow airlines to require documentation of a person's disability and say that the medical necessity of having the animal while traveling is understood.
The Department of Housing and Urban Development talks about assistance animals, which can include "providing emotional support to persons who have a disability related need for such support."
There's room for fraud and shady maneuvering here, Ensminger said. There have been cases where patients have written their own letters that psychiatrists have signed to recommend certifying a psychiatric dog. That's not how prescribing a treatment is supposed to work. There are also fake certification websites, Herzog said.
And it's not just a letter that turns a dog into a psychiatric service dog. There's a rigorous training procedure, and the whole process can cost as much as $38,000, Ensminger estimates.
Although some people try to train dogs themselves, this approach often fails because it takes a lot of expertise to choose the right dog, train it, and develop a relationship between a person and a service dog, said Darcie Boltz, executive director of Heeling Allies.
It takes a dog with a unique temperament to be properly suited for this work, and there can be animal welfare issues when improperly selected or trained dogs become mental health service dogs, Boltz said.
Although the system for psychiatric service dogs and emotional support animals can be abused, Lieberman says it's rare.
"If it isn't really important to you psychologically, there's so much hassle that you have to go through, you wouldn't necessarily ask for it," she said. "The solace of having your dog there to comfort you needs to be more important than the hassle you have to go through."
Lieberman recommends to her patients that dogs for mental health needs have some sort of identifying jacket so that there's less stigma and confusion around taking it to a place where animals usually aren't permitted.
The flip side
A bill passed by the Senate this month may restrict service dog access in the Veterans Affairs Department for people whose dogs did not come from accredited trainers, the Army Times reported.
Mental health support dogs also might lead to situations where people with the animals are on the same plane flight as people with severe pet allergies.
This is a problem for Sloane Miller, allergy advocate and life coach with severe asthma. She recalls that three years ago, she couldn't board her scheduled plane, or any other with the same airline to Florida that day, because emotional support animals were flying, too.
Miller supports service animals, but "it should be fair for everyone who has a need and a disability," she said. "There needs to be some kind of protection for my rights as well, to be able to travel in a safe environment."
And don't forget the animal's well-being, says Lori Marino, senior lecturer in psychology at Emory University. While it's a healthy path for some, there is concern that the animals themselves may be emotionally harmed. When dogs are paired with depressed and anxious people, the animals might become depressed and anxious, too.
Marino has worked with a homeless pet rescue, evaluating whether prospective pet owners are good matches for prospective dogs. Once in a while, a prospective owner will say, "I want this dog because I am depressed and need a pick-me-up," Marino said.
"I always decline that person. It's not fair to the dog to go to a home that's not emotionally healthy," she said. A dog "shouldn't be used as medicine."
But for people such as Hernandez and Aragon, dogs are medicine, a medicine that is keeping their PTSD in check. Hernandez has become a strong advocate for service dogs.