As of 2015, there is no required certification process for psychiatric service dogs in the United States, but a psychiatric service dog must undergo training to perform a specific task that assists its owner function with a diagnosed mental illness. Service dogs must also have basic obedience training and cannot behave aggressively.
The nature of task that service dogs can perform varies widely. Many psychiatric service dogs are trained to remind their owners to take necessary medication, while others may provide a protective barrier or a specific calming behavior during an anxiety attack. However, the dog's presence and instinctive calming behaviors alone are not enough to qualify an animal as a service dog. The assistance that the dog provides must be trained rather than emerge purely from instinct.
Dogs that provide general emotional support but do not have a trained task may qualify as emotional support animals. Emotional support animals do not have the same access rights as service animals, but they do have some special rights. They generally have special access to housing and public transportation where pets are not otherwise allowed.
Some states may have slightly different definitions of what qualifies as a service dog or emotional support animal, so owners should check local laws. However, those laws cannot be more restrictive than the guidelines set by the Americans with Disabilities Act, which is the federal legislation that defines what service and support animals are.