Introduction: Elevation in serum bilirubin concentration is associated with reduced risk of cardiovascular disease (CVD). Silymarin, an extract of the Milk Thistle plant, inhibits UGT1A1 enzymes, the main enzyme responsible for the conjugation and elimination of bilirubin from the body. This effect of elevated serum bilirubin may potentially protect against CVD. Aim/Objective: Using a single-blind, placebo-controlled crossover trial to investigate the in-vivo effects of Legalon®, on circulating bilirubin concentrations, platelet characteristics, and coagulation, recognised CVD biomarkers. Method: The effects of Milk Thistle (Silibinin) On circulating unconJugated bilirubin levels and markers of Oxidative stress and inflammation (MOJO) study was a randomised single-blind, crossover, placebo-controlled trial. The required number of participants, based on power calculation and basis of the trial was sixty-five participants. Participants were provided Legalon® and placebo during two supplementation phases, each of 14 days duration with a 28 day washout period in between. Demographic data and blood samples were collected during seven participant visits (screening, Day 0, Day 7, and Day 14 for each arm). Light transmission aggregometry, flow cytometry, clinical biochemistry, haematology, coagulation analysis, and high-pressure liquid chromatography (HPLC) were performed for collecting blood samples. Subsequent statistical analysis was conducted for seventeen participants who had satisfactory compliance (> 80% compliance for both study arms). Results: Twenty-five male participants were enrolled into the MOJO trial. Seventeen male participants completed the trial with satisfactory compliance (>80% for both the Legalon® and placebo capsules). Circulating total bilirubin (TB) and direct bilirubin (DB) showed no significant difference between time points, and between the study arms (TB ANOVA time p=0.8773, treatment p=0.8971; DB ANOVA time p=0.9210, treatment p=0.9849). This was confirmed with HPLC analysis. Platelet aggregation induced by no agonist (NA), collagen, adenosine diphosphate (ADP) and thrombin receptor-activating peptide (TRAP) did not significantly differ between time points, and between study arms (maximum aggregation (%) NA ANOVA time p=0.4672, treatment p=0.1946; collagen ANOVA time p=0.6387, treatment p=0.3527; ADP ANOVA time p=0.3740, treatment p=0.9956; TRAP ANOVA time p=0.5790, treatment p=0.2029). No significant difference in platelet activation was observed between the Legalon®-arm and placebo-arm in flow cytometry analysis (ADP CD62P ANOVA time p=0.2943, treatment p=0.6460; ADP PAC-1 treatment p=0.1093; TRAP CD62P ANOVA time p=0.3032, treatment p=0.7140; TRAP PAC-1 ANOVA time p=0.4070, treatment p=0.3103). However, a significant increase was observed for PAC-1 between Day 0 and Day 14, in response to ADP (ANOVA time p=0.0311). Mean platelet volume (MPV) and platelet count showed no significant change between time points and between the study arms (MPV ANOVA time p=0.2631, treatment p=0.6900; platelet count ANOVA time p=0.8766; treatment p=0.8766). Prothrombin (PT) and activated prothrombin time (aPTT) did not differ significantly between the study arms or between time points (PT ANOVA time p=0.8106, treatment p=0.9331; aPTT ANOVA time p=0.8106, treatment p=0.9331). Conclusion: The MOJO trial did not demonstrate significant changes to the primary or secondary outcomes. When compared to other clinical studies that utilised silymarin, the differences in silymarin preparation, the participants involved, duration of administration and dosage of the intervention may have contributed to these findings. Despite this, Legalon® capsules were taken at the prescribed dose, therefore, these results are important and challenge claims made by the manufacturer. The main limitation of the present study, includes that the sample size (17 participants), did not meet the required participant number (65 participants), as such this trial is underpowered. Secondly, the duration of Legalon® administration was another limitation as the two-week duration may have been too short in comparison to other clinical studies, who administered Silymarin for over a month. Other factors such as the poor bioavailability of Legalon®, time of blood collection, and variability in lifestyle may have contributed to the lack of significant findings. The MOJO trial remains an important field of research and challenges the manufacturer claims for this preparation and explored the in-vivo effects of silymarin on circulating bilirubin levels and its correlation to platelet characteristics, platelet function and coagulation in humans. Recommended changes to the MOJO trial include changing the silymarin preparation (silipide) and increasing participant recruitment. Initiating these changes may demonstrate a novel means to increase circulating bilirubin and therefore reduce CVD risk, which remains the world’s greatest cause of mortality.