A high percentage of new drug candidates fail to reach the market during clinical trials, and these failures imply massive financial losses for the pharmaceutical companies. Clinical trials have distinctive characteristics and additional complexity compared with the late stages of product development in many other industrial sectors. Although the current literature on clinical trial has offered explanations for why a drug is abandoned during clinical trials (e.g., toxicity, lack of efficacy, and economics), studies investigating non-drug-related causes of failure are scarce. New product development (NPD) failures also differ from one another; however, no comprehensive conceptual framework in the NPD literature describes how to classify failures. This study suggests a conceptual framework for explaining NPD failures in the pharmaceutical industry by drawing on clinical trial literature combined with an exploratory empirical approach based on 17 interviews with industry experts. The initial interviews were used to identify managerial issues related to clinical trial failure, and the later interviews had a more iterative character to validate the issues identified in the previous round. We identified seven critical management issues causing failures in clinical trials. Our findings indicate that chaotic and slow patient recruitment, lack of experience in choosing and monitoring partners, lack of feasibility of the study protocol, low quality of the registered data, too high incidence of serious adverse events and severe incidents, unmanageable level of portfolio complexity, and incorrect assessment of the market potential or returns cause the failure of clinical trials. The conceptual framework for failures proposed in this paper combines project and product failures while acknowledging relevant specificities in clinical trials. Clinical trial managers are also supported in their decision making in clinical trials with an identified list of critical management issues that require attention to reducing the chance of failure. This study provides a basis for future empirical testing, including measuring interdependencies among the critical management issues and their adequacy for predicting failure.