This document establishes a non-derogable boundary governing all intentional interventions into human consciousness, irrespective of substance, technology, device, platform, or declared intent. It fixes a minimum classificatory and ethical reference standard and prevents conceptual evasion through labeling, consent-based framing, or non-medical claims. Where such interventions become systematized, measured, data-driven, algorithmic, scaled, or commercialized, an automatic transition to the operational domain of the Consciousness–Aptamer Interface System (CAIS) occurs by function and effect. This Boundary operates independently of consent or adoption and is intended to be invoked in disputes, regulatory reviews, due diligence, or judicial proceedings. Detailed permissions, restrictions, and conditions of use following CAIS entry are governed separately under:“CAIS Licensing & Usage Covenant v1.0”.