Background
Red yeast rice (RYR), a natural lipid-lowering agent, is widely used in clinical practice. However, the existing meta-analyses concerning the safety of RYR preparations have yielded inconsistent results, and the credibility of the evidence has not been quantified.

Objective
This study was designed to evaluate the existing evidence and offer a comprehensive understanding of the associations between the use of RYR preparations and various adverse health outcomes.

Search strategy
Seven literature databases were searched from inception to May 5, 2023, using medical subject headings and free-text terms (e.g., “red yeast rice,” “Xuezhikang,” and “Zhibitai”).

Inclusion criteria
Meta-analyses that investigated and quantitatively estimated associations between the use of RYR preparations and adverse health outcomes were included in this study.

Data extraction and analysis
Two researchers independently extracted data using a standardized data collection table; any disagreements were resolved by consulting a third researcher. Based on the participant, intervention, comparator and outcome (PICO) framework in each eligible meta-analysis, a series of unique associations between the use of RYR preparations and adverse health outcomes were determined. The associations’ effect estimates were re-evaluated using random-effect models.

Results
Fifteen meta-analyses, comprising 186 (164 unique) randomized controlled trials, were identified. Based on A MeaSurement Tool to Assess Systematic Reviews version 2, 3 (20%) and 12 (80%) of these meta-analyses had low and critically low confidence, respectively. A total of 61 unique associations between the use of RYR preparations and adverse health outcomes were extracted from eligible meta-analyses. Based on the random-effect models, 10 (16.4%) associations indicated a significant protective effect of RYR preparations against adverse health outcomes, while 5 (8.2%) indicated an increased risk of adverse health outcomes related to uric acid, alanine transaminase and aspartate transaminase levels. The other 46 (75.4%) associations showed no significant difference between the use of RYR preparations and control treatments. Regarding the credibility of the evidence, 21 (34.4%), 34 (55.7%) and 6 (9.8%) associations showed moderate, low and very low credibility, respectively.

Conclusion
The evidence examined in this study suggests that RYR preparations are safe; however, the credibility of the evidence was not high. Further high-quality evidence is required.

Key words: Red yeast rice, Safety, Adverse health outcomes, Umbrella review, Meta-analysis, Systematic review