This is a non-therapeutic, Phase 1 clinical trial to examine the safety, pharmacokinetic (PK) characteristics, and pharmacodynamics (PD) effect of indole-3-carbinol (I3C) and silibinin (Sil) in healthy subjects.

Inclusion Criteria:

• Adult ≥ 18 years old

• Current smoker of ≥ 8 cigarettes per day for at least the last 6 months by self-report

• Adequate blood counts, and adequate liver and kidney function defined as follows:

  • Hemoglobin ≥ 9 g/dL for women, ≥ 10 g/dL for men
  • Platelet count ≥ 100 x 10^9/L
  • Total bilirubin ≤ Institutional upper limit of normal (≤ 1.3 mg/dL for UMMC)
  • ALT ≤ 1.5 times institutional upper limit of normal
  • Creatinine ≤ 1.4 g/dL and estimated GFR ≥ 80 mL/min/1.7m2

• Able to understand the experimental nature of the study and provide informed written consent

Exclusion Criteria:

• Chronic proton pump inhibitor, H2-blocker (i.e., ranitidine, famotidine), and/or calcium carbonate use
• History of gastric bypass surgery, gastric banding, bowel resection, malabsorption syndromes such as celiac sprue or pancreatic insufficiency, or other conditions that may affect gastric or intestinal absorption of nutrients
• Current use of tobacco products other than cigarettes (i.e. snuff, snuz, smokeless tobacco, cigars, pipes), or use of these products within 3 months of study registration
• Major or chronic medical disease, including heart disease, poorly controlled diabetes, etc., to be adjudicated by the principal investigator
• Known active malignancy
• History of aerodigestive malignancies
• Women who are pregnant, intend to become pregnant within 3 months of study registration, or who are lactating. Women of childbearing potential must have a negative urine pregnancy test within 14 days of starting the assigned intervention
• Antibiotic use within 2 months of study registration by self-report
• History of respiratory tract cancer
• Known allergy to I3C, Sil, or its components
• Psychiatric and/or social situations that would potentially limit compliance with study requirements