I find Terrence McKenna's argument that consciousness is demonstrably entangled in the material world at a quantum mechanical, atomic level convincing. To summarize, it is known that two similar chemical compounds, differing only in the placement of a single atom on the carbon ring structure of a molecule, when administered in doses at the order of micrograms will either be psychoactive and result in a massive disruption to the human subject's baseline consciousness or be inert beyond our ability to measure an effect.
That provides precisely no evidence that consciousness is somehow related to events on the quantum level. We know why drugs have the effects they do - because the brain has receptors specifically calibrated to accept or reject molecular inputs. But those inputs are chemical, not quantum - they are not indeterminate, they are lynchpins in chains of chemical reactions.
You omit that if you give a much larger dose of the same thing you'd kill a person, and a smaller dose might fall below any threshold of activity at all.
And for that matter, a microgram is a huge quantity of matter.
