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&NA; The entropic brain hypothesis proposes that within upper and lower limits, after which consciousness may be lost, the entropy of spontaneous brain activity indexes the informational richness of conscious states. Here the hypothesis is revisited four years on from its original publication. It is shown that the principle that the entropy of brain activity is elevated in the psychedelic state is increasingly well supported by separate and independent studies and analyses, and evidence for greater brain criticality under psychedelics is also highlighted. It is argued that heightened brain criticality enables the brain to be more sensitive to intrinsic and extrinsic perturbations which may translate as a heightened susceptibility to “set” and “setting”. This updated version of the original entropic brain hypothesis now offers more concrete information on specific measures of brain entropy and suggests new studies to scrutinise it further, as well as examine its utility for describing and informing the treatment of psychiatric and neurological conditions such as depression and disorders of consciousness. This article is part of the Special Issue entitled ‘Psychedelics: New Doors, Altered Perceptions’. HighlightsReference to specific measures of entropy thought to meaningfully index the qualia of conscious states, e.g. Lempel‐Ziv.A specific example of a clinical problem (namely disorders of consciousness) where the entropic brain hypothesis may inspire a novel intervention.How heightened brain criticality confers maximal sensitivity to perturbation via intrinsic or extrinsic sources (“set” and “setting).How there may be an upper bound to the entropic brain principle beyond which unconsciousness occurs.How recent findings on brain serotonin encoding behavioural responses to uncertainty mesh well with the entropic brain hypothesis.