The gemarah (Bava Metziah 32b, based on Shemot 32:5) explains that a person is not allowed to give an animal undo pain, this is know as צער בעל חי. I would like to know if a person is allowed to give an animal drugs for recreational purposes? For example catnip or pot brownies for a dog. On the one hand I am not aware of any halacha this would violate (see this summary of the halachot of caring for pets) and there is evidence that animals do things to intentionally get high on their own. On the other hand it is possible that the animal will injure itself after taking the drugs (I am unsure if grama would be applicable in this type of case) thereby causing (indirectly) pain to the animal, it is also possible that the drugs cause the animal pain and we are not aware of it. Furthermore, it is possible that the drugs could have an adverse long term effect on the animals brain, especially if the animal gets high multiple times.