Phytochemicals are bioactive natural compounds extracted from plants. Phytochemicals have been considered as a major resource for developing non-toxic agents in prevention and treatment of chronic diseases, such as diabetes and cancer. However, most phytochemicals have low absorption rates, and the dose levels necessary for their beneficial effects can barely be achieved in the body after oral consumption, which limits their effect in humans. Therefore it is in urgent need to identify phytochemicals of higher uptake rate (or termed bioavailability). Arctigenin is a novel anti-inflammatory lignan mainly existing in the seeds of the herb Arctium lappa. This herb particularly its seeds has been widely used in traditional Chinese medicine to treat inflammation-related diseases such as cold, sore throat, and cough. The anti-cancer activity of arctigenin has recently been identified in cultured cancer cells and in animal models of several cancers. In prostate cancer, we found that arctigenin is highly effective in inhibition of the growth of cultured prostate cancer cells, while without affecting normal cells. The strong anti-tumor activity of arctigenin was further confirmed in our animal studies with prostate cancer mouse models. By analysis of blood concentrations of arctigenin, we found that the effective dose of arctigenin as observed in cultured cancer cells was achievable in mouse blood after consumption of arctigenin at a safe level, which suggests that the bioavailability of arctigenin is adequately high for its anti-cancer effect in organisms. We therefore propose a phase I one-arm dose escalation study to confirm the safety and bioavailability of arctigenin in healthy men, and to determine the dosage for future phase II studies in prostate cancer prevention. The study will use the traditional 3+3 design, which is the most widely used phase I design in oncology. Three dose levels of arctigenin will be tested, and participants will receive two capsules of arctigenin per day for 28 days, each capsule containing 250 mg of arctigenin. Initially there will be three participants on each dose level. If there is no dose-limiting toxicity (DLT) observed in any participant, the dose will be escalated to the next level. If DLT is observed in one or two participants, three more participants will be added. If DLT is observed in one or two participants out of the six, the dose will be escalated to the next level. If DLT is observed in three or more participants of the six, the previous dose level will be considered as the maximally tolerated dose (MTD), and three more patients will be added to the MTD group for a more accurate evaluation of the safety. The estimated MTD is the highest dose level with observed toxicity rate less than 0.33. Blood samples will be collected at baseline, during week 2 and on the last day of the study. Urine samples will be collected once a week during the intervention. On the last day of the intervention (Day 28) we will perform a single dose challenge with arctigenin and collect blood at baseline and at 1h, 2h, and 3h after arctigenin consumption in the morning. Arctigenin and its glucuronide will be analyzed in blood and urine using high performance liquid chromatography (HPLC)