AEBM Stack Extension: Multi-Compound Burden-to-Yield Analysis for Anabolic-Androgenic Steroid Stacks - A Mathematical Extension of the AEBM Framework with Domain Interaction Coefficients, Diminishing Functional Yield and Uncapped Systemic Burden Aggregation

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 percent 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. Methods: This paper introduces Stack_BYR as an extension of the AEBM framework with three methodological elements: (1) domain-specific interaction coefficients (K_d) modelling burden amplification across five consolidated system domains (N, CV, H, HEM, EM); (2) uncapped systemic burden aggregation (SBB), restoring discriminative power across realistic stack configurations; (3) a diminishing-returns function for Stack Functional Yield (SFY) with ordinal weights 1.00, 0.40, 0.20, 0.10. Results: Ten representative stack configurations were analysed. Stack_BYR values range from 0.96 (testosterone + drostanolone) to 2.68 (testosterone + nandrolone + trenbolone + boldenone). Trenbolone as a K_N = 1.40 amplifier dominates the neuropsychiatric profile of any stack in which it appears. Conclusions: Stack_BYR is a systemic parameter, not a sum of component BYRs. Stack_BYR values are not directly comparable to per-compound BYR values in the AEBM FOA Extension due to different domain structures and scales; explicit nomenclature guidance is provided in Section 3.4.