Here is a wiki referencing him.
[en.wikipedia.org]
"Although it has been assumed that this crown was blue because it was fashioned to represent the sky, another theory [8] implies that this crown was fashioned to represent the pileus of an entheogenic mushroom, commonly known as a Psilocybe, that turns blue when touched, deducibly because ingesting this mushroom led the shamanic ancestors of Egyptian pharaohs to believe that they were divine and immortal. Accordingly, the theory also implies that Egyptian pharaohs later wore this crown, knowingly or unknowingly, as a remnant of the entheomycological origin of their divinity and immortality, and Egyptian myth-makers and artists later personified the spirit of the deity that seemingly resided in this mushroom as the blue-headed deity Osiris. Since serpents were ubiquitously associated with mushrooms in antiquity, ancient Egyptian artists often placed a serpent on this crown as another remnant of its mycological origin and significance."


Here is a wiki not referencing him. It links to a CDC page.
[en.wikipedia.org]
"The ancient Egyptians considered mushrooms food for royalty.[8]"