Valium etc. (diazepam) is a benzodiazepine medication used in pets to treat anxiety disorders and seizures.
Benzodiazepines like diazepam act by enhancing the actions of a natural brain chemical, GABA (gamma-aminobutyric acid). GABA is a neurotransmitter, a chemical that carries messages between brain nerve cells. GABA inhibits the transmission of nerve signals, thereby reducing nervous excitation.