An Early Phase 1 interventional study of Oregano and Drug cocktail in Interaction, sponsored by Washington State University. Recruiting at 1 site in United States. Open to participants aged 18 Years to 64 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-06-04.
Sponsored by Washington State University · Early Phase 1, Interventional, and Basic science
The purpose of this clinical trial is to determine how the supplement oregano affects how the body metabolizes pharmaceutical drugs.
Oregano (Origanum vulgare) is a flowering plant native to Europe. The fresh or dried leaves are commonly used as a cooking herb. Oregano oil extracts are also marketed as herbal supplements. O. vulgare ranked as the number 12 top-selling herbal supplement in the natural channel in 2022. Oregano supplements are consumed for myriad purported medicinal properties, including antimicrobial, antioxidant, and anti-inflammatory effects. Oregano contains multiple types of compounds, including phenols, terpenes, and terpenoids. Recent compelling in vitro data showed that an extract of O. vulgare activated the human pregnane X receptor (PXR) and aryl hydrocarbon receptor (AhR), which regulate the expression and activity of the prominent drug metabolizing enzymes cytochrome P450 (CYP) 3A4 and CYP1A2, respectively. PXR also regulates the expression and activity of several other CYPs (e.g., CYP2C9, CYP2C19), as well as transporters (e.g., the efflux transporter P-glycoprotein (P-gp)). The extent of activation of both receptors by O. vulgare rivaled that of St. John's wort, a well-known herbal supplement that induces CYP and P-gp activity in human participants. These investigators next evaluated the effects of O. vulgare on CYP3A4 and CYP1A2 activity in human hepatocytes. Again, the extent of induction by O. vulgare rivaled that of St. John's wort. Collectively, these observations suggest that oregano supplements could precipitate numerous interactions with pharmaceutical drugs.
The primary objective of the proposed study is to evaluate the potential for a well-characterized O. vulgare product to precipitate pharmacokinetic interactions with a "cocktail" of oral drugs that are substrates for multiple CYPs. The investigators and others have shown this validated cocktail (caffeine, dextromethorphan, losartan, midazolam, and omeprazole) to be safe to administer to healthy adult participants. The secondary objective is to determine the pharmacokinetics of the oregano supplement, which to date have not been rigorously characterized in humans. Results will be used to help inform healthcare practitioners and consumers about the safe use of this increasingly popular herbal supplement when consumed with certain pharmaceutical drugs.
Washington State University is the lead sponsor of 83 studies on the registry; 16 are open to participants now.
Of its 7 completed or terminated interventional studies of FDA-regulated products, 4 (57%) have results posted.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
6 participants will be administered 180 mg of a well-characterized oregano product. Blood will be drawn via an indwelling venous catheter immediately before and at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, and 24 hours after administration of oregano. Urine will be collected in multiple jugs for 24 hours.
Dietary Supplement: Oregano
16 participants, which may or may not include any number of the original 6 from Arm 1, will be administered an oral drug cocktail consisting of caffeine (100 mg), dextromethorphan (30 mg), losartan (25 mg), midazolam syrup (2 mg), and omeprazole (20 mg). Blood and urine will be collected in the same manner described in Arm 1.
Drug: Drug cocktail
The same 16 participants will be administered the oregano product and the drug cocktail. Blood and urine will be collected in the same manner described in Arm 1.
Dietary Supplement: Oregano · Drug: Drug cocktail
The same 16 participants will self-administer the oregano product at home for 5 consecutive days. On day 6, participants will return to the study setting, where the procedure described in Arm 3 will be repeated.
Dietary Supplement: Oregano · Drug: Drug cocktail
Oil of oregano administered as a softgel (180 mg).
Drug pages: Caffeine · Warfarin · Dextromethorphan · Midazolam · Omeprazole · Vitamin K 1
Oral drug cocktail consisting of caffeine (100 mg), dextromethorphan (30 mg), losartan (25 mg), midazolam syrup (2 mg), and omeprazole (20 mg).
Midazolam Area under the plasma concentration vs. time curve (AUC) ratio
Ratio of the area under the plasma concentration vs. time curve of midazolam in the presence to absence of oregano.
Time frame: 0-24 hours
Caffeine AUC ratio
Area under the plasma concentration vs. time curve of caffeine in the presence to absence of oregano.
Time frame: 0-24 hours
Caffeine maximum plasma concentration (Cmax) ratio
Ratio of the maximum plasma concentration of caffeine in the presence to absence of oregano.
Time frame: 0-24 hours
Caffeine half-life ratio
Ratio of the half-life of caffeine in the presence to absence of oregano.
Time frame: 0-24 hours
Dextromethorphan AUC ratio
Area under the plasma concentration vs. time curve of dextromethorphan in the presence to absence of oregano.
Time frame: 0-24 hours
Dextromethorphan Cmax ratio
Ratio of the maximum plasma concentration of dextromethorphan in the presence to absence of oregano.
Time frame: 0-24 hours
Dextromethorphan half-life ratio
Ratio of the half-life of dextromethorphan in the presence to absence of oregano.
Time frame: 0-24 hours
Losartan AUC ratio
Ratio of the area under the plasma concentration vs. time curve of losartan in the presence to absence of oregano.
Time frame: 0-24 hours
Losartan Cmax ratio
Ratio of the maximum plasma concentration of losartan in the presence to absence of oregano.
Time frame: 0-24 hours
Losartan half-life ratio
Ratio of the half-life of losartan in the presence to absence of oregano.
Time frame: 0-24 hours
Midazolam Cmax ratio
Ratio of the maximum plasma concentration of midazolam in the presence to absence of oregano.
Time frame: 0-24 hours
Midazolam half-life ratio
Ratio of the half-life of midazolam in the presence to absence of oregano.
Time frame: 0-24 hours
Omeprazole AUC ratio
Area under the plasma concentration vs. time curve of omeprazole in the presence to absence of oregano.
Time frame: 0-24 hours
Omeprazole Cmax ratio
Ratio of the maximum plasma concentration of omeprazole in the presence to absence of oregano.
Time frame: 0-24 hours
Omeprazole half-life ratio
Ratio of the half-life of omeprazole in the presence to absence of oregano.
Time frame: 0-24 hours
Plan to share: Yes — IPD used in the results publication
No publications or documents are linked to this record.
Started Sep 2024 (actual). Primary completion is estimated for Dec 2026, 26 months after the start.
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Studies of the drugs tested here: Caffeine · Warfarin · Dextromethorphan · Midazolam · Omeprazole · Vitamin K 1
Washington State University