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Effects of Garlic Supplements on Drug Metabolism

This study has been completed.
ClinicalTrials.gov Identifier:
First Posted: July 22, 2005
Last Update Posted: January 1, 2010
The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details.
National Center for Complementary and Integrative Health (NCCIH)
Information provided by:
Fred Hutchinson Cancer Research Center
July 20, 2005
July 22, 2005
January 1, 2010
July 2005
Not Provided
Blood plasma and urine samples [ Time Frame: 3 months ]
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Complete list of historical versions of study NCT00122889 on ClinicalTrials.gov Archive Site
Blood plasma and breath samples. [ Time Frame: 3 months ]
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Effects of Garlic Supplements on Drug Metabolism
Garlic Metabolism and Cytochrome P450 Modulation
This study will determine whether garlic supplements affect the way certain drugs are processed in the body.

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.

Observational Model: Case-Only
Time Perspective: Prospective
Not Provided
Retention:   Samples With DNA
Whole blood, urine
Non-Probability Sample
Healthy volunteers
  • Drug: Garlic powder with high allicin content
  • Drug: Garlic powder with low allicin content
  • Drug: Garlic oil
  • Drug: Aged garlic
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*   Includes publications given by the data provider as well as publications identified by ClinicalTrials.gov Identifier (NCT Number) in Medline.
March 2009
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Inclusion Criteria:

  • Body mass index (BMI) between 20 and 32
  • Able to read and understand English

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
Sexes Eligible for Study: All
18 Years to 45 Years   (Adult)
Contact information is only displayed when the study is recruiting subjects
United States
R21AT002712-01 ( U.S. NIH Grant/Contract )
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Danny Shen, PhD, Fred Hutchinson Cancer Research Center
Fred Hutchinson Cancer Research Center
National Center for Complementary and Integrative Health (NCCIH)
Principal Investigator: Danny D. Shen, PhD Fred Hutchinson Cancer Research Center
Fred Hutchinson Cancer Research Center
December 2009