Constructing the Unpaid Price How U.S. List Prices Are Engineered Never to Transact: The PBM Gross-to-Net Fallacy and the Emerging IRA/MFN Pricing Environment

Background. U.S.-branded drug list prices, Wholesale Acquisition Costs (WAC), anchor every downstream reimbursement formula, yet match the transaction price for essentially no payer. The gap between list and net revenue, the "gross-to-net bubble," reached an estimated $356 billion for brand drugs in 2024. This review asks how manufacturers build the WAC, why it systematically overstates the Average Sales Price (ASP), the realized net price, and how the Inflation Reduction Act (IRA) and the 2025 Most-Favored-Nation (MFN) executive order alter that logic Methods. Because realized net prices and rebate splits reside in confidential commercial contracts and cannot be pooled, the study is a gray-literature review using structured narrative synthesis rather than meta-analysis. This effort involved screening and selecting sources following a PRISMA-informed process and tiered by reliability: Tier 1 primary government and legal records, Tier 2 peer-reviewed methodology and policy journals, and Tier 3 trade institutes and consultancies. Each cited claim traces to a digital object identifier (DOI), PubMed identifier (PMID), or official URL. The analysis traces one artifact, the WAC, across construction, divergence, and policy compression. Results. Manufacturers construct the WAC through five frameworks. These include analog benchmarking, quality-adjusted life -year (QALY) value modeling, willingness-to-pay research, discounted cash flow (DCF) recovery, and strategic rebate room engineering. These function not as independent checks but as a rationalization stack producing the maximum defensible price. The resulting list-to-net divergence is structurally inevitable. Five forces (the Medicaid best-price trap, escalating rebate walls, 340B volume growth, the IRA Part D manufacturer discount, and access barriers) drive realized ASP to 40-60% of WAC, or below, in highly rebated classes. Patients pay cost-sharing on the inflated anchor while intermediaries capture the rebate. First-round Medicare negotiations cut prices by 38-79% below the list price. The MFN order anchors U.S. prices to the lowest gross domestic product (GDP)-adjusted price among comparable nations, dismantling each pillar of the construction architecture. Conclusions. The gross-to-net gap is not a market inefficiency. Instead, it represents a system operating as designed, with the list price serving as an instrument for rebate generation. The IRA and MFN compress the headroom on which that logic depends. However, patients benefit only if WAC falls and policymakers redesign cost-sharing around the net price. The structural transformation is real. Its distribution is not yet determined. The review contributes 1) a unified causal account linking list-price construction, the rebate economy, and the 2022-2026 policy rupture; 2) a tiered, verifiability-governed gray-literature method for a domain whose decisive data are confidential; and 3) a literature-to-question mapping that makes the evidence base for each research question explicit and auditable.