|Valerian - Photo by helen.2006 (Flickr)|
The roots and leaves of valerian have a similar effect on cats as the much better known catnip. Valerian contains a chemical called actinidine. It has a similar effect on cats as the chemical nepetalactone, which is found in catnip.
Both are called "cat attractants" by the Wikipedia authors. We know what some cats do when they smell catnip. It's a kind of mild, safe, recreational drug for the domestic cat.
Associated: Unified Catnip Theory and The Cat Drugs of Catnip and Matatabi.