Background: The original AEBM (System-Specific Burden Matrix) analyses biological cost and functional yield for individual anabolic-androgenic steroid (AAS) compounds. Since more than 80% of AAS users employ multi-compound combinations, the linear sum of per-compound BYR values does not adequately represent actual systemic burden in stacked protocols. Pharmacological interactions between compounds produce non-additive amplification of burden in specific physiological domains that cannot be captured by simple summation. Methods: This paper introduces Stack_BYR as an extension of the AEBM framework, incorporating:- Domain Interaction Coefficients (K_d): empirically derived multipliers that model non-linear burden amplification when compounds share overlapping toxicity pathways- Diminishing Functional Yield: logarithmic saturation model for androgenic signal when multiple compounds target the same receptor system- Uncapped Systemic Burden Aggregation: burden accumulates without ceiling, reflecting clinical reality of compounding toxicity The model enables quantitative comparison of multi-compound AAS protocols based on their net functional yield relative to total systemic biological cost. Application: Stack_BYR provides a formal, reproducible basis for protocol evaluation in harm reduction and clinical advisory contexts. Example analyses are provided for common stacking patterns including testosterone + nandrolone, testosterone + trenbolone, and triple-compound combinations. Author: Jakub Czernikiewicz, CZERNIHealth (czernihealth.pl)