I have a friend, not a close friend but a friend, who is a therapist. A couple days ago she asked me a question. She said she sometimes has clients that ask her to please write them a letter saying they need their pet to be a service dog so they can take their dog into public places. They say their dog helps their depression or anxiety, so they want their dog to be a service dog. She was wondering if a dog is really a service dog if it just makes someone feel better or feel less anxious or less depressed.
It's a great question. The answer is no, if all the dog does is provide comfort or emotional support, it's not a service dog. It might be an emotional support animal, but it's not a service dog.
A service dog must be trained to perform specific tasks that mitigate a person's disability. And the person must be disabled in order to have a service dog. Not everyone that suffers from anxiety, depression or other psychological problems is disabled by their condition.
An emotional support animal is a pet (doesn't have to be a dog) belonging to a person with a psychiatric disability (like anxiety or depression) that is recommended by their doctor, therapist or other healthcare provider as part of their treatment plan. Again, the person must be disabled, and not everyone with anxiety or depression is disabled by their condition.
Service dogs have to be trained to perform specific tasks to mitigate a person's disability but emotional support animals don't need any special training.
Service dogs are allowed to go most places with their handlers, including restaurants and stores. Emotional support animals are not. In most cases, landlords must allow people to have emotional support animals, even if they do not normally allow pets (some landlords are exempt from this law, however), and people are allowed to fly within the U.S. with an emotional support animal in the cabin of the plane. Same goes with service dogs. You cannot take an emotional support animal to a restaurant, grocery store, hotel that does not allow pets, doctor's office, movie theater, etc. though, unless you get permission from the manager (and in some cases, the manager cannot legally give permission; health codes prevent them from allowing an emotional support animal in a restaurant, for instance).
You don't need a letter from your therapist to take your service dog into public places. In fact, it is illegal for business owners to ask to see such a letter. If you are disabled and your dog is trained to perform tasks that mitigate your disability, then you are allowed to take your service dog with you.
If you are not disabled, though, or if your dog is not trained to perform actual tasks that mitigate your disability, even if you have a letter from your therapist, you are not legally allowed to take your dog into public places where pets are not permitted. A letter from your therapist does not override the law.
If you have an emotional support animal, you may be required to provide a letter from your therapist or other healthcare provider in order to fly with your emotional support animal or in order to live in no pets housing with your emotional support animal.
Here are links to some articles with more information about emotional support animals:
Where Can You Take Your Emotional Support Animal?
Keeping an Emotional Support Animal in an Apartment that Doesn't Allow Pets
Flying with an Emotional Support Animal