Though catnip is a stimulant for cats, the plant has the opposite effect on dogs and is sometimes used as a sedative or nerve tonic for them. If your dog gets nervous when going to the vet or in the car, for example, try putting a few fresh catnip leaves in his drinking water. You can also sprinkle some dried catnip -- 1/8 to 1/2 teaspoon of per pound of food -- on his food or mix in some catnip tea.