Plain English Summary
Background and study aims
Chemicals known as furanocoumarins (8-methoxypsoralen [8-MOP] and 5-methoxypsoralen [5-MOP]) are known to inhibit the breakdown (metabolism) of caffeine. However, it is not known if ingestion of herbs containing these chemicals will have the same effect. The aim of this study is to determine if a single meal of furanocoumarin-containing herb (or vegetable) would cause inhibition of caffeine metabolism after co-administration.
Who can participate?
Healthy volunteers aged 20 - 35 years (non-smoker, not pregnant or breastfeeding).
What does the study involve?
Collection of timed saliva and urine samples from you after ingesting caffeine tablets (200 mg) alone and caffeine tablets (200 mg) with an herb (or vegetable) together (total caffeine consumption by you is 400 mg for the whole study).
What are the possible benefits and risks of participating?
You will not benefit directly from this study. No information or results obtained by this study will be made available to you. However, there is the potential to benefit other people in the future if the study leads to the development of an effective method for predicting caffeine/herb interaction using in vitro data.
There will be no risk to your health because the amount of caffeine ingested is equivalent that in a cup of coffee. Moreover, the herbs (or foods) selected for the study are found in our daily diets. Please note that caffeine overdose only occurs when large amount of caffeine (more than the recommended dose by Health Canada) is ingested. Caffeine overdose may result in adverse health effects including nausea, vomiting, irritability, nervousness, anxiety, panic attacks, dehydration, and sleep disorders in sensitive individuals (Health Canada, 2012).
Where is the study run from?
Department of Biological Sciences, Simon Fraser University, BC, Canada
When is the study starting and how long is it expected to run for?
June 2012 to June 2016
Who is funding the study?
1. Simon Fraser University, Canada
2. Global Collaborative Research, King Abdullah University of Science and Technology
Who is the main contact?
Dr Zeyad Alehaideb
Caffeine/Angelica dahurica and caffeine/Salvia miltiorrhiza metabolic inhibition in humans: In vitro and in vivo studies.
Caffeine metabolism (CYP1A2-Mediated) can be modulated by pre-consumption of two Chinese medicines of Danshen (Salvia miltiorrhiza) and Baizhi (Angelica dahurica).
Approved 20/09/2012, Simon Fraser University Office of Research Ethics Committee (Discovery 2 building, 8900 Nelson Way, Burnaby BC V5A 4W9; +1 firstname.lastname@example.org), ref: 2012s0565
Interventional (cross-over) single center
Primary study design
Secondary study design
Non randomised study
Patient information sheet
See additional files
Participants are asked to refrain from ingesting caffeine, caffeinated drinks and furanocoumarin-containing foods for 3 days before and after participating in the first pharmacokinetic study (without co-treatment with an herb) and until the end of the second pharmacokinetic study (with co-treatment of an herb). Participants are provided with a study kit consisting of caffeine tablets (400 mg), an herbal extract, and several coded containers for saliva and urine sample collection. Participants conduct the studies in the home:
First pharmacokinetic study:
Time course of caffeine and metabolite concentrations in the saliva of humans without herb/food extract co-treatment. On the day of the experiment, ingest 200 mg caffeine tablets (equivalent to the amount of caffeine in a cup of coffee or in a can of energy drink). A saliva sample (about 3 ml) will be collected in a coded, siliconized glass tube just before dosing. Serial saliva samples also will be collected at 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8 and 12 hr post-dosing. A 30 ml urine sample will be collected at 4-8 hr post caffeine administration since the half-life of caffeine clearance in the human is about 4-4.5 hr.
Second pharmacokinetic study:
Time course of caffeine and metabolite concentrations in the saliva of humans co-treated with an herb/food extract. After a 3-day wash-out period, ingest 4.5 g (or 9 g) of a dehydrated herb (or food) in the form of an aqueous extract 3 hr before ingesting the caffeine tablets. One of the following herbs or vegetables: parsnip, celery, dill, parsley, angelica, false bishop’s weed, common rue, lovage, khella, dong quai, and baizhi. A saliva sample (about 3 ml) will be collected in a coded, siliconized glass tube just before dosing. Serial saliva samples also will be collected immediately after dosing with an herb extract at 0.5, 1, 1.5, 2.5, 3.0 hr and after dosing with 200 mg caffeine at 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8 and 12 hr. 30 ml urine samples will be collected before dosing and at 4-8 hr post-caffeine ingestion.
Caffeine; herbal whole aqueous extract of either Danshen (Salvia miltiorrhiza) and Baizhi (Angelica dahurica).
Primary outcome measure
Caffeine concentrations in human saliva collected at 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8 and 12 hr post-dosing using liquid chromatography
Secondary outcome measures
Caffeine concentrations in urine collected 4 - 8 hours post-dosing
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
Aged 20-35 years
Target number of participants
Participant exclusion criteria
2. On medication
3. Pregnant or breast feeding
3. Any health issue(s) that would affect the results of the study
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Simon Fraser University
Department of Biological Sciences Simon Fraser University
Department of Biological Sciences, Simon Fraser University
B.C. Canada V5A 1S6
King Abdullah International Medical Research center
Department of Medical Genomics
King Abdullah International Medical Research Center
P.O. Box 3660
Simon Fraser University
Funding Body Type
Funding Body Subtype
Global Collaborative Research, King Abdullah University of Science and Technology
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
To be published in thesis and journals.
IPD sharing statement:
The datasets generated during and/or analysed during the current study are not expected to be made available due to the raw data not being available.
Intention to publish date
Participant level data
Available on request
Basic results (scientific)
A. dahurica and S. miltiorrhiza extracts were capable of inhibiting caffeine metabolism in human subjects. In a separate study, cytochrome (CYP) 1A2-mediated caffeine demethylase activity was studied in incubation containing human liver microsomes, β-nicotinamide adenine dinucleotide phosphate, and an herbal extract (or a pure bioactive chemical from the herbs). In all cases, CYP1A2 activity was decreased with an increasing inhibitor concentration, confirming the inhibition of caffeine metabolism in vivo. Caffeine metabolism inhibition most likely involved the competitive and/or non-competitive mechanism.
- ISRCTN83028296_PIS_20Sept12.pdf Uploaded 11/06/2019