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Animals increasingly are being used to assist patients with mental disorders, as evidence grows that they can help people with autism, PTSD and other conditions function in their everyday lives.

The assistants are usually dogs but sometimes can include miniature horses, chinchillas or other animals.

Some are highly trained psychiatric-service animals that, for example, might help autism patients improve their social skills and interactions.

Others are household pets called emotional-support animals, or ESAs, a fast-growing type, partly because they require no special training, just a doctor's note saying the pet helps the patient. Some owners of emotional-support animals say having the pets allows them to reduce how much medication they take. But ESAs also have spurred controversy, in part because some airlines and restaurants that typically bar pets will permit entrance to emotional-support animals, a development that is seen to encourage abuse.

There is no national certification program or registration for any type of assistive animal.

Annie Roeder, 29, of Palm Beach Gardens, Fla., has dissociative disorder, a condition that involves sporadic memory loss, feelings of detachment from oneself and perceptions that people and objects aren't real. She says her psychiatric-service dog, Bamboo, a basset hound-beagle mix, helps her when she is having an anxiety attack or feels out of touch with reality. The dog alerts Ms. Roeder when the episode is occurring and will lay down on her lap to stabilize her. Ms. Roeder says she doesn't know whether Bamboo is detecting a change in her actions or something else. "He just knows" when an attack is coming, she says.

Ms. Roeder says she used to be afraid to spend much time in public in case she had a dissociative episode. But since getting Bamboo 2½ years ago she now feels safe to engage in regular activities outside her home.

Identifying health benefits from animal-assisted therapy, as the field is known, comes mostly from observational studies, as the practice doesn't lend itself to traditional randomized, controlled experiments. And for designations like emotional-support animals, where there isn't training or regulation, the lack of standards makes it difficult to study the effects on health.

Still, the pool of studies that have been done increasingly suggests that animal-assisted techniques can be beneficial, says James Serpell, director of the Center for the Interaction of Animals and Society at the University of Pennsylvania. He says some research indicates that animal interventions can help encourage social interactions and reduce behavioral outbursts in some children with autism-spectrum disorders as effectively as other conventional treatments, including cognitive-behavioral therapy. However, the animal techniques are less effective than other methods at helping with conditions such as anxiety, depression or fear, the research has shown.

"The balance points to these types of interventions working surprisingly well for some groups," says Dr. Serpell.

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