Pot for pets

So, quick background. My four year old dog has chronic pain in his back legs. He constantly has trouble getting up and down, and he whines when he is trying to stand up. But some days it doesn't hurt as much and he's able to play. We've taken him to the vet and the medication didn't really help at all. So my boyfriend and I thought, if marijuana helps with pain, maybe it would with dogs too. I'm not talking the whole joint with him but lit blow a hit into his face. Does anyone think this could help?