The rising costs of prescription drugs present a major challenge to healthcare systems, leading many payers to adopt risk-sharing or managed entry agreements to mitigate financial uncertainties. This study introduces an analytical framework that incorporates physicians' imperfect adherence to prescribing guidelines in the design of such agreements. Physicians are categorized into three groups based on their adherence levels, impacting the decision-making of both public payers and pharmaceutical manufacturers. Using a Stackelberg game framework, we model the interactions where the manufacturer first sets the drug price, and the payer subsequently determines access conditions to maximize net monetary benefit (NMB). Our findings reveal that deviations from prescribing guidelines significantly alter equilibrium outcomes, influencing optimal pricing, coverage thresholds, and stakeholder incentives. We also examine how different risk-sharing mechanisms interact with physician behavior, shaping payer expenditures, manufacturer profits, and patient access. These insights underscore the necessity of accounting for prescribing heterogeneity in pharmaceutical pricing policies to ensure cost-effective and equitable access to medications.