^Why?
I'm not sure about every country, but in North America (and likely most or all "first world" countries), veterinary medications are usually no different from their human counterparts, aside from the dosages/strengths in some cases, or medications or formulations that don't exist for human use of course. In the US, USP-approved animal pharmaceuticals are often made in the same manufacturing plants as human pharmaceuticals and will contain the same ingredients. They are often even the same color, shape, and bare the same markings as human drugs. If it's a pill, you can look up the pill description (shape, colour, imprint) on a pill ID site and see what comes up. If it has a USP Verified Pharmaceutical Ingredient Mark on the packaging, it means it is the same drug that a doctor would prescribe for a human. If a pill looks exactly like the human version, then it is the same thing, because the FDA forbids 2 pills to have identical appearance/markings unless they have identical contents. Certain animal medications might not be made to the same standards as a human medication, for example medications produced for livestock and intended to be mixed with feed might have impurities in them, but those made for household pets are usually as safe for human consumption as their human counterparts. A drug that is a different formulation from the human version might contain different inactive ingredients, for example flavourings that would appeal to dogs.
There have been cases of animal drugs being used in US prisons because there was a shortage of the human version.
As for veterinary Tramadol, it should be as safe for humans to take as the human version of Tramadol. I know the 50mg tablets are exactly the same as the human 50mg Tramadol. I have not seen the 12mg ones. Is it possible a vet could have compounded them? There are some veterinary compounding pharmacies that do make tablets. Personally I would be shocked if they contained anything unsafe for humans. Check the ingredient list and make sure they don't contain any other active ingredients or anything.
Of course, this is all assuming you meant is the animal Tramadol any less safe for humans than regular human Tramadol, and not if the question was is Tramadol safe period. Taking any drug has risks of course and I would not call Tramadol harmless.
EDIT: As for dosage, the receommended dose is 50-100 mg (which can be taken again 4-6 hours later) and the maximum dose is 400 mg/day. If you have never taken opioids or Tramadol before I would start with 50mg your first time to see how it affects you. And read up on the side effects and contraindications.
. I figured you were sort of joking about the "apart from ketamine" part, but I thought you were being serious about the rest because a lot of people assume veterinary medications are dangerous for humans to take (which is a perfectly understandable assumption and what the authorities want us to think so that we don't take them, and they can certainly be dangerous if misused, whereas if you have to get a prescription for something and go to the pharmacy for it, that at least decreases misuse). Pet meds do often say "not for human consumption" but that is for legal reasons. Of course I would never take an animal drug that is not approved for human use at all, like bovine growth hormone or flea and tick killer or something 
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