I thought tegratol was an epilepsy medicine, but are some people using it for chronic pain?

Yes. Neuroleptics are a general class of drugs that have their primary act ion on nerve cells, or particular neurotransmitters (the chemical released at the end of one neuron activating the next neuron). Since none that we have purely affect a specific nerve cell or a specific transmitter or just one part of the brain, clinically one drug can be useful for multiple disorders, as in case u asked.
Used for both. Its mechanism of action allows its use for both plus psych disorders plus weight loss plus probably other things too.