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

November 4, 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

Completed

Conditions

Intervention / Treatment

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

Interventional

Enrollment (Actual)

16

Phase

  • 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 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

Ages Eligible for Study

18 years to 64 years (Adult)

Accepts Healthy Volunteers

Yes

Genders Eligible for Study

All

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
Intervention / Treatment
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
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

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Nicotine AUC
Time Frame: 0-12h

Nicotine Area Under the Curve alone and in the presence of cinnamon
0-12h

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Letrozole AUC
Time Frame: 0-240h

Letrozole Area Under the Curve alone and in the presence of cinnamon
0-240h
Letrozole Cmax
Time Frame: 0-240h

Letrozole maximum concentration alone and in the presence of cinnamon
0-240h
Nicotine Half Life
Time Frame: 0-12h

Nicotine half life alone and in the presence of cinnamon
0-12h
Nicotine Cmax
Time Frame: 0-12h

Nicotine maximum concentration alone and in the presence of cinnamon
0-12h
Letrozole Half Life
Time Frame: 0-240h

Letrozole half life alone and in the presence of cinnamon
0-240h

Collaborators and Investigators

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

Sponsor

Washington State University

Collaborators

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)

December 14, 2021

Primary Completion (Actual)

August 31, 2023

Study Completion (Actual)

August 31, 2024

Study Registration Dates

First Submitted

December 1, 2021

First Submitted That Met QC Criteria

December 1, 2021

First Posted (Actual)

December 15, 2021

Study Record Updates

Last Update Posted (Actual)

November 5, 2026

Last Update Submitted That Met QC Criteria

November 4, 2026

Last Verified

November 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID 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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