Psilocin (the active form your body makes from psilocybin) slips into the brain because its hydroxyl sits at position 4, not 5, letting it fold into a hidden internal hydrogen bond that masks its polarity and sneaks it past the blood-brain barrier. Move that same oxygen one spot over and you get bufotenine, which barely gets in at all. Psilocin runs a 2–3 hour half-life with effects lasting 5–7 hours, and the review flags sub-psychedelic psilocin doses now being tested for mood and sleep without the full trip.