Limitations
There are a number of limitations to our review. Relevant articles might be missed because the search was conducted only in three databases, in one language, and excluded grey literature. One article about the protective effect of ginkgo biloba extract on CiO was retrieved by the manual research on clinicaltrial.gov, but wasn’t available in its full-text format. The conclusions of our review are based on studies with small and heterogeneous samples, who were followed on different time ranges, and whose analysis had low quality, so our results should be taken as preliminary findings that need to be corroborated in the future. None of the trials took into account patients’ quality of life or reported outcomes to assess the intervention’s benefit. So a comprehensive understanding of the effectiveness of any intervention is missing. Finally, the safety outcomes of the interventions were not mentioned in 10 out of 23 studies. Since most of the interventions contain mild benefits and uncertain risks, underreporting of side effects limits the power of our conclusions.