THC is generally considered the element of marijuana that gets you high. Think paranoid, incompetent, impaired memory, depleted motor control effects. You could almost consider THC to be the bad side effect of marijuana.
Most days people who are using marijuana for medicinal benefits rather than a recreations drug are looking for the CBD. Is is not a psychoactive like THC. This is why it would effect dogs completely differently. Given their (usually) smaller stature to humans, the way they metabolize, and their neurological differences to humans. Now I’m going a little out of my knowledge here, but I presume these differences is why large amounts of THC can be devastating to dogs. Frankly large amounts of THC, IMO, are not that great for people either. CBD does not effect neurological pathways nearly to the likes of THC.
People who regularly take CBD report great things. Personally I tend to use it to reduce nausea, and arthritis pain, and sometimes for focus (take my experience for what it’s worth). CBD does not make you sleepy like THC, either. CBD has also been tested mildly on animals and so far has been deemed ‘safe’ at large doses. The UK tends to do more studies than the US due to federal regulations.
I also know a few people who administer CBD therapy to some of their animals who are having end of life medical problems, and they’ve felt like it’s reduced their animal from puking, given a bit of energy… Who knows it might just be a placebo effect or the owner just wants to see a change.
That might be a lot of information, but essentially the take away from all of that is THC is bad because it effect neuralgic pathways, and CBD is alright because it does not effect the body neurologically. However we don’t really know how CBD effects the body due to lack of studies.