Antipsyhotics are the major tranquilizers class. They are prescribed to people with no mental illness as well for insomnia, so yes normal people can take them. They are also used as add ons to antidepressants with people with no Bipolar. And again they are used for schizophrenia and schizoaffective disorder and probably a few other uses in their as well, making it impossible to dx based on reaction.

People usually build a tolerance to them and the dose increases to achieve the same effect. And the tolerance can build quite quickly. 600 mg is quite a lot but I have seen people on pretty high doses of seroquel who appear to be functioning. I have bipolar 1 with psychotic episodes and could not tolerate more than 200 or so mg's and could not function at all, so it really does depend on the person.