When I first got Katy, she had severe separation anxiety. Before I learned how to keep it under control with a few basic training techniques we tried everything from calming herbal supplements to melatonin. I also left her with Genius Kongs filled with frozen food, made sure to walk her extra, and even tried little pep talks. So, in a desperate attempt to try to fix her anxiety problems, we started using the Thundershirt.
Pros: Although this might not matter to some people, the Thundershirt is really cute. I was also impressed with the fact that even when Katy was very anxious, my little Houdini could never wiggle herself out of the shirt or damage it.
Cons: I did not see a huge difference using the Thundershirt at first, but I think that was partially due to the fact that her anxiety levels were off the charts. It took a long time to see any results, but now that Katy has calmed down significantly, when I begin to see her getting anxious, I do use the shirt. It was definitely not the miracle that was promised, but it has been a little helpful.
Summary: If you are looking for something to be a magic cure for anxiety, try exercise and lots more exercise. The Thundershirt did not give us huge results, but I would recommend it to help as part or a plan to deal with less severe anxiety.