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Effects of Garlic Supplements on Drug Metabolism

This study has been completed.
National Center for Complementary and Integrative Health (NCCIH)
Information provided by:
Fred Hutchinson Cancer Research Center Identifier:
First received: July 20, 2005
Last updated: December 30, 2009
Last verified: December 2009
This study will determine whether garlic supplements affect the way certain drugs are processed in the body.

Condition Intervention Phase
Drug: Garlic powder with high allicin content
Drug: Garlic powder with low allicin content
Drug: Garlic oil
Drug: Aged garlic
Phase 4

Study Type: Observational
Study Design: Observational Model: Case-Only
Time Perspective: Prospective
Official Title: Garlic Metabolism and Cytochrome P450 Modulation

Resource links provided by NLM:

Further study details as provided by Fred Hutchinson Cancer Research Center:

Primary Outcome Measures:
  • Blood plasma and urine samples [ Time Frame: 3 months ]

Secondary Outcome Measures:
  • Blood plasma and breath samples. [ Time Frame: 3 months ]

Biospecimen Retention:   Samples With DNA
Whole blood, urine

Enrollment: 80
Study Start Date: July 2005
Study Completion Date: March 2009
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.


Ages Eligible for Study:   18 Years to 45 Years   (Adult)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   Yes
Sampling Method:   Non-Probability Sample
Study Population
Healthy volunteers

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
  Contacts and Locations
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Please refer to this study by its identifier: NCT00122889

United States, Washington
Fred Hutchinson Cancer Research Center
Seattle, Washington, United States, 98109
Sponsors and Collaborators
Fred Hutchinson Cancer Research Center
National Center for Complementary and Integrative Health (NCCIH)
Principal Investigator: Danny D. Shen, PhD Fred Hutchinson Cancer Research Center
  More Information

Responsible Party: Danny Shen, PhD, Fred Hutchinson Cancer Research Center Identifier: NCT00122889     History of Changes
Other Study ID Numbers: FHCRC-1984.00
R21AT002712-01 ( US NIH Grant/Contract Award Number )
Study First Received: July 20, 2005
Last Updated: December 30, 2009

Keywords provided by Fred Hutchinson Cancer Research Center:
Drug Interactions
Complementary Therapies
Complementary and Alternative Medicine

Additional relevant MeSH terms:
Allyl sulfide
Anti-Infective Agents
Hypolipidemic Agents
Molecular Mechanisms of Pharmacological Action
Lipid Regulating Agents
Protective Agents
Physiological Effects of Drugs
Hypoglycemic Agents
Free Radical Scavengers
Anticarcinogenic Agents
Antineoplastic Agents
Cytochrome P-450 Enzyme Inhibitors
Enzyme Inhibitors processed this record on May 24, 2017