The suspension of clinical trials during the COVID-19 pandemic has been discussed widely. But no systemic study has examined the crowding-out effect of COVID-19 on the clinical trials of non-COVID-19 diseases under a well-recognized disease classification system. By acquiring disease-specific trials data from ClinicalTrials.gov and Dimensions, this study explores the crowding-out effect of COVID-19 from the aspects of trials' activeness and efficiency, as well as the scientific collaboration from multiregional clinical trials (MRCTs). In addition to global observation, the USA, China, Japan, the UK are chosen as representative examples to conduct a more fine-grained comparative analysis. Interestingly, our analysis did not reveal substantial crowding-out effects of the COVID-19 pandemic on medical research resources for other diseases. Specifically, the impact of COVID-19 on the quantity of trials for non-COVID-19 diseases varied significantly across nations, in which China displays a pattern that is considerably different from the other three nations. Further, even though the intensified attention on COVID-19 research has been observed, the progression and completion of other diseases' trials has not been significantly impacted by the pandemic. The examination of MRCT also shows that throughout the pandemic, clinical science collaboration among countries has also been intensified.