Well, it's not just Occam's razor, but abductive reasoning or the appeal to the best explanation. The problem is that this appeal to what's more likely depends on our background beliefs. What seems more likely to you and to me will differ if our background beliefs differ. The epistemic question then would revert to whether our fundamental beliefs which are determining those probability judgments were acquired responsibly or somehow problematically.
Sure, biologists would have to explain how the brain can hallucinate the psychedelic experience. What's more unlikely, though, that some such explanation could be given, that complex patterns can arise from simpler ones, or that we communicate with supernatural beings by taking drugs? If the former really seems less likely to you, that must be because you've grown accustomed to accepting the paranormal or the supernatural. Scientists more often than not haven't.