Effects of Garlic Supplements on Drug Metabolism


This study will determine whether garlic supplements affect the way certain drugs are processed in the body.

Full Title of Study: “Garlic Metabolism and Cytochrome P450 Modulation”

Study Type

  • Study Type: Observational
  • Study Design
    • Time Perspective: Prospective

Detailed Description

Garlic supplements, which are often used to lower cholesterol and prevent cancer, are one of the most commonly used herbal products in the United States. However, little is known about the way garlic supplements may interact with prescription medications when used simultaneously. This study will investigate four commonly used garlic supplements: garlic powder with a low content of allicin (a compound with antibacterial properties), garlic powder with a high allicin content, garlic oil, and aged garlic. The effects of these 4 garlic products on the drug-metabolizing enzyme cytochrome P450 (CYP) and a drug transporter, P-glycoprotein (Pgp) will be examined. Participants will be randomly assigned to receive one of the four garlic supplements for 4 weeks. Drug probes of CYP and Pgp will be used to assess the in vivo activities of the substances. On the first day of garlic ingestion, blood collection will occur immediately after participants ingest their garlic supplement and 3, 4, and 6 hours after ingestion. Urine collection will occur immediately after participants' first garlic ingestion and 12, 15, and 72 hours after ingestion. Blood and urine collection will determine the concentration of the drug probes in the body, which will indicate changes in CYP and Pgp. Blood and urine tests will be repeated at the end of the study.


  • Drug: Garlic powder with high allicin content
  • Drug: Garlic powder with low allicin content
  • Drug: Garlic oil
  • Drug: Aged garlic

Clinical Trial Outcome Measures

Primary Measures

  • Blood plasma and urine samples
    • Time Frame: 3 months

Secondary Measures

  • Blood plasma and breath samples.
    • Time Frame: 3 months

Participating in This Clinical Trial

Inclusion Criteria

  • Body mass index (BMI) between 20 and 32 – Able to read and understand English – MUST LIVE WITHIN THE SEATTLE, WA AREA. Exclusion Criteria:

  • Current use of herbal medicines other than oral contraceptives – History of cardiopulmonary, liver, renal or endocrine disease – Allergy or sensitivity to any of the drugs that will be used in the probe cocktails or the garlic supplements – Daily consumption of vegetables with a high allium content, including garlic, shallots, leeks, and chives – Pregnancy or breastfeeding

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: 45 Years

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • Fred Hutchinson Cancer Center
  • Collaborator
    • National Center for Complementary and Integrative Health (NCCIH)
  • Provider of Information About this Clinical Study
    • Danny Shen, PhD, Fred Hutchinson Cancer Research Center
  • Overall Official(s)
    • Danny D. Shen, PhD, Principal Investigator, Fred Hutchinson Cancer Center

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