Beta blocker and Thorazine (chlorpromazine) in combination can increase the risk of hypotension. I regularly see people prescribed both however.
'Some antipsychotic agents and some beta-blockers may mutually inhibit each other's metabolism resulting in increased or additive pharmacologic effects such as hypotension, bradycardia, delirium or seizures. The mechanism may be related to competitive inhibition of CYP450 2D6-mediated first-pass metabolism.'