Could a common spice change how drugs work in your body?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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