Here's one piece of evidence out of thousands more. Consider that the psychedelic effects of LSD can be prevented simply by blocking 5-HT2A receptors in the brain [1]. This is what you would expect if a psychedelic experience is a biochemical phenomenon occurring in the brain, like that sparked by caffeine. A more powerful and much more interesting one, yes, but not something that requires talking of "god" or "universal understanding".
[1] https://blogs.scientificamerican.com/scicurious-brain/httpbl... (search the page for "block the 5-HT2A receptor")
Even though neuroscience intimidates me, I'm smart enough to regurgitate the summary: "The 5-HT2A receptor is central to the effects of many psychedelics, but it may not be the only receptor involved." Also I know enough about myself that I don't kknow any of these topics enough to evaluate Barbara E. Bauer, or https://psychedelicreview.com. I can keep Googling though ...
This was quite interesting news: https://psychedelicreview.com/uc-berkeley-opens-the-center-f...