Once a disease develops, it is difficult to restore to health. Therefore, disease prevention is important to extend healthy life expectancy. In this study, we propose a computational method to estimate the potential preventive drugs that are effective in preventing the onset of the target disease by calculating the reporting odds ratio based on the reports of clinical medication history (more than 40 million reports on drug responses and adverse events). Since the potential preventive drugs were overlooked by conventional odds ratios, we calculated a variant of the odds ratio in order to overcome the problem of the conventional odds ratio, and analyzed the mode-of-action of the preventive drugs based on the chemical structures and chemical-protein interactome. We applied the proposed method to various diseases including hypertension, and evaluated its performance in terms of reproducibility for known therapeutic targets. We confirmed that the proposed odds ratio worked better than the conventional odds ratio. The proposed method is applicable to any diseases and is expected to useful for prevention for various diseases.