Evaluating the Pharmacokinetics and Drug Interaction Potential of the Botanical Dietary Supplement Cinnamon

August 20, 2026 updated by: Mary Paine, Washington State University
The purpose of this study is to evaluate a well-characterized, commercially available cinnamon dietary supplement as a precipitant of pharmacokinetic interactions with cytochrome P450 (CYP) 2A6 drug substrates in healthy volunteers. Nicotine gum will be used as the CYP2A6 probe drug (i.e., positive control) and letrozole as a high-impact object drug. Results will be used to inform future research on the potential use of cinnamon as a smoking cessation agent, as well as the clinical impact on pharmacotherapeutic regimens involving letrozole in cancer patients.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Completed

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

Cinnamon is used worldwide as both an additive and a botanical dietary supplement, the latter of which ranked within the 30 top-selling herbal supplements in 2020. Cinnamon is added to a variety of products, ranging from foods (e.g., breakfast cereals, baked goods) to fragrances and essential oils, to improve taste or smell. As a dietary supplement, cinnamon is commonly used to lower blood sugar and reduce inflammation. Cinnamon contains the abundant component, cinnamaldehyde (CA), a phenylpropanoid that emanates the flavor and scent of cinnamon. Research by Harrelson and colleagues has shown CA to inhibit the drug metabolizing enzyme cytochrome P450 (CYP) 2A6 in a time-dependent manner. That is, CYP2A6 metabolizes CA to a reactive intermediate that destroys the enzyme. Such substrates are also referred to as "suicide substrates". This type of enzyme inhibition is similar to that of grapefruit juice, which contains furanocoumarins that are time-dependent inhibitors of CYP3A in the intestine, leading to numerous potential adverse interactions with drugs metabolized by CYP3A. Unlike competitive inhibitors, time-dependent inhibitors inactivate the enzyme permanently, requiring de novo synthesis of the enzyme. As such, drug interactions with time-dependent inhibitors can last for several days. Relative to CYP3A, the list of clinically relevant CYP2A6 substrates is very short. However, two critical substrates include nicotine and the anticancer agent letrozole. Using an in vitro-to-in vivo extrapolation approach, CA was predicted to increase the area under the plasma concentration vs. time curve (AUC) of both substrates by 4- to 5-fold exceeding the FDA recommended cutoff (1.25) These compelling observations prompted this clinical study.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Actual)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
16

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Early Phase 1

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

Study Locations

  • United States
    • Washington
      • Spokane, Washington, United States, 99202
        • Washington State University College of Pharmacy and Pharmaceutical Sciences

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

18 years to 64 years (Adult)

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Males and females, aged from 18-64 years and healthy
  • Not taking any medications (prescription and non-prescription) or dietary/herbal supplements known to alter the pharmacokinetics of either study drug or cinnamon constituents
  • Willing to abstain from consuming dietary/herbal supplements and citrus juices for several weeks
  • Willing to abstain from consuming caffeinated beverages or other caffeine-containing products the evening before and morning of the first day of a study arm
  • Willing to abstain from consuming any alcoholic beverages for one day prior to any study day, during the 14-hour inpatient days, and for the outpatient visit(s) following the 14-hour visit
  • Willing to use an acceptable method of contraception that does not include oral contraceptive pills or patches (such as abstinence, copper IUD, condom)
  • Have the time to participate
  • Written informed consent (and assent when applicable) obtained from subject or subject's legal representative and ability for the subject to comply with the requirements of the study

Exclusion Criteria:

  • Under the age of 18 or 65+ years
  • Any current major illness or chronic illness such as (but not limited to) kidney disease, hepatic disease, diabetes mellitus, hypertension, coronary artery disease, chronic obstructive pulmonary disease, cancer, or HIV/AIDS
  • History of anemia or any other significant hematologic disorder
  • History of drug or alcohol addiction or major psychiatric illness
  • Pregnant or nursing
  • History of allergy to cinnamon, letrozole, or nicotine
  • Taking concomitant medications, both prescription and non-prescription (including dietary supplements/herbal products), known to alter the pharmacokinetics of either study drug or cinnamon constituents
  • Presence of a condition or abnormality that, in the opinion of the Investigator, would compromise the safety of the patient or the quality of the data
  • Recreational drug use such as amphetamines, benzodiazepines, cocaine, marijuana, MDMA, opioids, and PCP
  • History of intolerance to cinnamon
  • Out-of-range clinical laboratory value that the study physician considers participation in the study a health risk

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Basic Science
  • Allocation: Non-Randomized
  • Interventional Model: Crossover Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: Letrozole
Arm 3 will consist of administration of a single oral dose of letrozole (2.5 mg) to the same 16 subjects who participate in Arm 2. Blood and urine will be collected from 0-240 hours and 0-24 hours, respectively, relative to letrozole administration. Participants will undergo a washout of at least 14 days before beginning Arm 4.
Drug: Letrozole (2.5 mg)
tablet, 2.5 mg
Other Names:
  • Femara
Experimental: Cinnamon + Nicotine
The same 16 subjects will self-administer the cinnamon product (2 g) three times daily for five consecutive days. On the sixth day, subjects will be administered cinnamon (2 g) and nicotine gum (2 mg). Cinnamon will be administered two additional times. Blood and urine will be collected from 0-12 hours relative to nicotine administration. Participants will undergo a washout of at least 4 days before beginning Arm 5.
Dietary supplement: Cinnamon (2 g)
oral capsules, 2 g
Drug: Nicotine gum (2.5 mg)
gum, 2.5 mg
Other Names:
  • Nicorette
Experimental: Cinnamon + Letrozole
The same 16 subjects will self-administer the cinnamon product (2 g) three times daily for five consecutive days. On the sixth day, subjects will be administered cinnamon (2 g) and letrozole (2.5 mg). Cinnamon will be administered two additional times. Blood and urine will be collected from 0-240 hours and 0-24 hours, respectively, relative to letrozole administration.
Dietary supplement: Cinnamon (2 g)
oral capsules, 2 g
Drug: Letrozole (2.5 mg)
tablet, 2.5 mg
Other Names:
  • Femara
Experimental: Cinnamon
Arm 1 will consist of administration of a single dose of cinnamon (2 g) with water by mouth to 6 subjects (3 males, 3 females). Blood will be drawn from 0-48 hours. Urine will be collected from 0-24 hours. The subjects may or may not elect to participate in Arms 2-5. If they do, a washout of at least 7 days will occur between Arm 1 administration of cinnamon and the Arm 2 administration of nicotine.
Dietary supplement: Cinnamon (2 g)
oral capsules, 2 g
Experimental: Nicotine
Arm 2 will consist of administration of a single dose of nicotine gum (2 mg) to 16 subjects. If these subjects participated in Arm 1, they will have completed a washout of 7 days since administration of cinnamon before starting Arm 2. Blood and urine will be collected from 0-12 hours relative to nicotine administration. Participants will undergo a washout of at least 4 days before beginning Arm 3.
Drug: Nicotine gum (2.5 mg)
gum, 2.5 mg
Other Names:
  • Nicorette

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Nicotine area under the concentration vs. time curve (AUC) ratio (exposure/baseline)
Time Frame: 0-12 hours
Ratio of the AUC of nicotine in the presence to absence of cinnamon.
0-12 hours

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Cinnamon constituent area under the concentration vs. time curve (AUC)
Time Frame: 0-48 hours
AUC of cinnamon constituents
0-48 hours
Cinnamon constituent maximum concentration (Cmax)
Time Frame: 0-48 hours
Cmax of cinnamon constituents
0-48 hours
Cinnamon constituent half-life
Time Frame: 0-48 hours
Time to reach one-half of the concentration of cinnamon constituents
0-48 hours
Cinnamon renal clearance
Time Frame: 0-24 hours
Renal clearance of cinnamon constituents
0-24 hours
Letrozole area under the concentration vs. time curve (AUC) ratio (exposure/baseline)
Time Frame: 0-240 hours
Ratio of the AUC of letrozole in the presence to absence of cinnamon.
0-240 hours
Nicotine and letrozole maximum concentration (Cmax) ratio (treatment/control)
Time Frame: 0-240 hours
Ratio of the Cmax of nicotine or letrozole in the presence to absence of cinnamon.
0-240 hours
Nicotine and letrozole half-life ratio (treatment/control)
Time Frame: 0-240 hours
Ratio of the time to reach one-half of the concentration of nicotine or letrozole in the presence to absence of cinnamon.
0-240 hours
Nicotine and letrozole renal clearance ratio (treatment/control)
Time Frame: 0-24 hours
Ratio of the renal clearance of nicotine or letrozole in the presence to absence of cinnamon.
0-24 hours

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Washington State University

Collaborators

Collaborators

An organization other than the sponsor that provides support for a clinical study. This support may include activities related to funding, design, implementation, data analysis, or reporting.
National Center for Complementary and Integrative Health (NCCIH)
Office of Dietary Supplements (ODS)

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
December 14, 2021

Primary Completion (Actual)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
August 31, 2023

Study Completion (Actual)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
August 31, 2024

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
December 1, 2021

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
December 1, 2021

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
December 15, 2021

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
August 24, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
August 20, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
August 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 18686
  • U54AT008909 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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