There are three known criteria that underlie drug reimbursement decisions: therapeutic value, cost-effectiveness, and burden of disease. However, evidence from recent reimbursement decisions in several jurisdictions points to residual, unexplained variables, among which is budget impact. Budget impact refers to the total costs that drug reimbursement and use entail with respect to one part of the health care system, pharmaceutical care, or to the entire health care system, taking into account the possible reallocation of resources across budgets or sectors of the health care system. The economic and equity rationale for carrying out budget impact analyses is opportunity cost, or benefits forgone, measured in terms of utility or equitable distribution, by using resources in one way rather than another. In other words, by choosing to draw down the budget in one way, decision makers forgo other opportunities to use the same resources. Under a set of unrealistic assumptions, cost-effectiveness analysis accounts for opportunity cost while conveying to the decision maker the price of maximizing health gains, subject to a budget or resource constraint. However, the underlying assumptions are implausible, particularly in the context of pharmaceutical care. Moreover, budget impact analysis is more useful to the decision maker than cost-effectiveness analysis if the objective is not to maximize health gains subject to a budget or resource constraint, but to reduce variance in health gains. With respect to equitable distribution, budget impact analyses lay bare the individuals or groups who lose out — those who bear the opportunity cost of spending resources in accordance with one decision rule rather than another.