I usually don't do reviews, but on this product, I decided to make an exception. I have a 12 year old Cairn Terrier who has had behavior issues combined with unexplained anxiety since we rescued her when she was 2 1/2 years old from a puppy mill. Vet after vet visit and different vets over the years, they could not help her. Prozac or Valium was useless. In October of 2009, after exhausting what we thought was all we could do for her, I decided to take her to the teaching hospital at the vet school. After two days of examination, they referred me to one of their animal behavioral vets. She gave me tips on how to relate to my dog, but she also gave me simple layman tools that anyone can do. She recommended we try the Anxitane S for her. I started her on it once a day for a week, then increased it to twice a day. She also started wearing a D.A.P. pheromone collar which has helped. The Anxitane S has proven to be the BEST thing that has helped my dog's anxiety. I am sure that the D.A.P. collar in combination with the Anxitane is a plus, but I know that the Anxitane is what has changed not only my dog's life for the better, but for the rest of us as well. This is a nutraceutical, not a pharmaceutical. L-Theanine is found naturally in green tea, which is known to have a calming effect. I do recommend having a vet supervise taking this even though you don't have to have a prescription. Sometimes, it takes more than one thing; to help with anxiety. A combination of several holistic therapies might be the trick. I can't say enough good things about this product.