Rescue Remedy is a Bach Flower essence. Dr. Bach was a reknowned British doctor practicing in the 1800s. He became frustrated with the limitations of allopathy (traditional) medicine and began experimenting with homeopathy and flower essences for treating his patients.
He found that combining five flower essences, a formula was created that worked to sooth the mind and relax the senses. This is the Rescue Remedy which is marketed off-brand as Five Flower Formula. This became the most famous of his remedies. Most natural foods and supplement stores carry it.
The human formula is carried in an alcohol base, which some dogs are sensitive to - mine aren't, but if you are concerned they make a pet formula that is alcohol-free.
I wrote an article about it with links to buy it online
Rescue Dogs | CupOFdog | Dog Site for Dog People