Cannabis can have tremendous benefits for sick creatures, but veterinarian Dr. Andrew Springer Browne, who has treated numerous pets that got a hold of their owners’ pot brownies, warns that animals should never ingest THC. Via the The New Inquiry:
Yes, an animal can get high on marijuana, but I would call it a very bad trip rather than being stoned or high.
The main clinical signs in dogs are low body temperature, dilated pupils, increased sensitivity to noise and movement, being unsteady on their feet. The animals are usually distressed and whimpering or howling. With really high doses they are collapsed, with a slow heart rate, barely responsive. This can last 24 to 48 hours. Usually they survive.
I would say though that any amount of marijuana is too much for an animal. Also, marijuana can have a variable amount of THC in it and also may contain contaminants like fungal spores, pesticides, or fertilizer.