Oil of Oregano With Black Seed Oil: Benefits, Risks

No trial has tested oil of oregano with black seed oil together, so the combination's benefits and safety are unknown; what exists is research on each oil alone. Black seed oil has 82 randomized trials in 5,026 people showing modest cardiometabolic changes¹, while oil of oregano has only a few small human studies².

The bigger issue is safety: thymoquinone, black seed's main compound, blocked a liver enzyme that clears warfarin and phenytoin in lab tests^{3, 4}. If you take prescription medicines, check with a pharmacist first.

The evidence for each oil is very different in size and quality, so look at them separately.

Black seed oil: modest, well-studied effects

Black seed (Nigella sativa) is the better-researched half. Pooled trials report these average changes:

• Blood pressure: systolic down 3.06 mmHg and diastolic down 2.69 mmHg⁵. See high blood pressure.
• Blood sugar: fasting glucose and HbA1c fell across 30 trials, with no change in insulin or insulin resistance⁶. See type 2 diabetes.
• Weight: about 2.09 kg more weight loss than placebo in adults with overweight or obesity, rated moderate certainty⁷.
• Inflammation and antioxidants: lower CRP and TNF-alpha and higher total antioxidant capacity across 20 trials in 1,086 adults, but no change in IL-6⁸.
• Cholesterol: LDL, total cholesterol and triglycerides improved in the 82-trial review¹. Our black seed oil for cholesterol page covers the detail.

These results come with a warning label: heterogeneity was very high, with I-squared values of 85% to 97% in the glucose and blood pressure analyses^{6, 5}. That means the trials disagreed a lot about how big the effect was.

Oil of oregano: promising in the lab, thin in people

Carvacrol, oregano's main compound, kills E. coli, Salmonella and other bacteria in lab tests, but a 2018 review found human trials still lacking². The human data are small and short:

• Cholesterol: in a 14-day randomized trial of 34 athletes, two carvacrol-rich oregano oils raised HDL compared with no oil; total cholesterol and triglycerides did not change⁹. See oil of oregano for cholesterol.
• Minor infections: a 10-day study of people with metabolic syndrome and bacterial infections (106 including an untreated control group) reported that oregano oil reduced minor infections without intestinal side effects; there was no placebo group¹⁰.

Is it different for men or women?

No. None of the studies above reported sex-specific benefits for either oil, so claims aimed at men or women are marketing, not findings. The same goes for seasonal immune or respiratory support, a common label claim that none of these trials tested.

Related health goals

• Blood Pressure Regulation
• Blood Sugar Balance
• Weight Loss Support
• Cholesterol Management

No. A PubMed search for black seed with oregano oil returned no human or animal studies of the pair, so "synergy" claims on labels are untested.

The closest data is a 2014 study of 104 people with small intestinal bacterial overgrowth (SIBO). One herbal option contained 0.1 mL of oregano oil per capsule, with thyme, sage and lemon balm, taken alongside a berberine blend for 4 weeks¹¹. Breath tests normalized in 46% on herbs versus 34% on rifaximin, a difference that was not significant¹¹. It contained no black seed, and the multi-herb mix makes it impossible to credit oregano alone. Our oil of oregano for SIBO page reviews it in full.

Not reliably, as far as the evidence shows. Each oil has one small old study, and neither had a placebo group.

• Oregano oil: 14 adults with gut parasites took 600 mg of emulsified oregano oil daily for 6 weeks. Blastocystis hominis cleared in 8 cases and symptoms improved in 7 of 11 people who had it¹².
• Black seed: in a 1991 field study, a single 40 mg/kg dose of the seeds cut tapeworm egg counts in children, a reduction not significantly different from the drug niclosamide's¹³.
• Against roundworm larvae: a 2025 lab study found that neither black seed nor oregano tinctures affected the survival of two parasitic nematode larvae¹⁴.

For black seed, the only human data is for tapeworms in that one study, and it tested the seeds, not the oil¹³. If you suspect intestinal parasites, a stool test identifies the organism, and prescription treatment is matched to it.

No study has compared morning and evening doses of either oil, so timing is your choice. Taking them with a meal is a sensible default if oils upset your stomach.

These are the amounts trials actually used:

• Black seed: 200 to 4,600 mg a day across 82 trials¹; 2 g a day of powder was used alongside H. pylori treatment for 8 weeks¹⁵.
• Oregano oil: 600 mg a day of an emulsified oil for 6 weeks¹², or 2 capsules twice daily of a blend for 4 weeks¹¹.

What to check on the label

Oregano oils in studies were standardized: 55% to 75% carvacrol in the SIBO blend¹¹, and 68% to 82% in the athlete trial⁹. A label that gives no carvacrol percentage tells you little about strength.

Black seed trials ran from 1 to 48 weeks¹. Oregano oil studies ran 10 days to 6 weeks^{10, 12}, so there is no safety data for months of daily use. A short course with a set end date fits the evidence better than open-ended use.

Black seed's effects were measured after weeks of daily use, not days¹. Expect nothing you can feel; the changes show up on lab tests and a blood pressure cuff.

Side effects in trials were uncommon, but case reports describe rare serious reactions to each oil.

• Digestive upset: one case of diarrhea among 37 people on herbal SIBO protocols, only some of which contained oregano oil¹¹.
• Allergy to oregano: one person had three systemic allergic reactions after eating oregano and thyme, with cross-reactions across the mint family¹⁶.
• Skin reactions to black seed oil: 3 people applying it to the skin developed severe blistering dermatitis with fever and over 15% skin detachment¹⁷.
• Kidneys: a 2013 case report linked acute kidney failure to black seed use in a person with diabetes¹⁸.
• Platelets: a 69-year-old woman taking black seed oil and evening primrose oil before surgery developed severe low platelets; the authors suspected the supplements made it worse¹⁹.

Case reports show what can happen, not how often. They are reasons to stop at the first rash or swelling, not reasons to panic.

Yes, black seed can. In human liver enzyme preparations (microsomes), thymoquinone blocked CYP2C9, the enzyme that clears many drugs, at very low concentrations³.

• Warfarin: lab modeling predicted that more than 1 g a day of black seed oil, or 18 mg of thymoquinone, might change warfarin levels⁴.
• Phenytoin: the same thresholds applied to this seizure drug²⁰.
• Diabetes medicines: black seed lowers fasting glucose and HbA1c, so it may add to glucose-lowering drugs⁶.
• Blood pressure medicines: its blood pressure effect could add to your medication's⁵. Our guide to blood pressure medicines and supplements covers this.
• Oregano oil: carvacrol is broken down mainly by CYP2A6, so drugs cleared by that enzyme could compete with it²¹.

These predictions come from lab and modeling studies, not from patients, so the risk is plausible but unconfirmed in patients.

Some people should skip it or ask a clinician first:

• People on blood thinners or seizure drugs: the CYP2C9 effect above^{4, 20}.
• People with diabetes or kidney disease: additive glucose lowering⁶, plus the kidney failure case report¹⁸.
• Anyone with a mint-family allergy: oregano cross-reacted with thyme, sage, marjoram and mint in allergy testing¹⁶.
• Anyone facing surgery: the platelet case occurred around a hysterectomy¹⁹.
• Pregnant or breastfeeding people and children: we found no human safety trials of either oil for these groups.

Doctors' caution has reasons. A 2021 review concluded that black seed and thymoquinone are still far from clinical use²². The trials are numerous but inconsistent, and the interaction data make doctors cautious with patients on several drugs³.

A simple rule based on the evidence above:

• If you want a cardiometabolic nudge: black seed alone has the trial data; adding oregano oil adds no proven benefit^{1, 2}.
• If you want to treat a gut infection or parasite: get tested first; the oil data are too small to replace treatment¹².
• If you take any daily prescription: ask your pharmacist about CYP2C9 before starting³.
• If you go ahead: use one product at a time for a few weeks, so you can tell which oil caused any reaction.

For more on plant-based antimicrobials, see our guide to natural antibiotics.

We searched PubMed for systematic reviews, randomized trials, case reports and interaction studies on black seed (Nigella sativa), thymoquinone, oregano oil and carvacrol, and for any study of the two together, which returned none. We read 22 study records and cited all 22, plus the full text of the 2014 SIBO study to confirm its oregano dose. We prioritized meta-analyses of randomized trials in adults; most oregano data are small, short or uncontrolled. Researched October 15, 2026.

1. Jafari A, et al. Does Nigella sativa supplementation improve cardiovascular disease risk factors? A comprehensive GRADE-assessed systematic review and dose-response meta-analysis of 82 randomized controlled trials. Pharmacol Res. 2025;219:107882. doi:10.1016/j.phrs.2025.107882 Our study summary.
2. Sharifi-Rad M, et al. Carvacrol and human health: A comprehensive review. Phytother Res. 2018;32(9):1675-1687. doi:10.1002/ptr.6103
3. Albassam AA, et al. Inhibition of cytochrome P450 enzymes by thymoquinone in human liver microsomes. Saudi Pharm J. 2018;26(5):673-677. doi:10.1016/j.jsps.2018.02.024
4. Wang Z, et al. Potential food-drug interaction risk of thymoquinone with warfarin. Chem Biol Interact. 2022;365:110070. doi:10.1016/j.cbi.2022.110070
5. Kavyani Z, et al. Antihypertensive effects of Nigella sativa supplementation: An updated systematic review and meta-analysis of randomized controlled trials. Phytother Res. 2023;37(8):3224-3238. doi:10.1002/ptr.7891 Our study summary.
6. Shirvani S, et al. The effect of Nigella sativa supplementation on glycemic status in adults: An updated systematic review and meta-analysis of randomized controlled trials. Prostaglandins Other Lipid Mediat. 2024;174:106885. doi:10.1016/j.prostaglandins.2024.106885 Our study summary.
7. Shahinfar H, et al. Comparative effects of nutraceuticals on body weight in adults with overweight or obesity: A systematic review and network meta-analysis of 111 randomized clinical trials. Pharmacol Res. 2023;196:106944. doi:10.1016/j.phrs.2023.106944
8. Kavyani Z, et al. The effect of Nigella sativa (black seed) on biomarkers of inflammation and oxidative stress: an updated systematic review and meta-analysis of randomized controlled trials. Inflammopharmacology. 2023;31(3):1149-1165. doi:10.1007/s10787-023-01213-0
9. Maral H, et al. Effect of Origanum dubium, Origanum vulgare subsp. hirtum, and Lavandula angustifolia essential oils on lipid profiles and liver biomarkers in athletes. Z Naturforsch C J Biosci. 2022;77(5-6):177-187. doi:10.1515/znc-2021-0142 Our study summary.
10. Ghitea TC, et al. The Antimicrobial Activity of Origanum vulgare L. Correlated with the Gastrointestinal Perturbation in Patients with Metabolic Syndrome. Molecules. 2021;26(2). doi:10.3390/molecules26020283 Our study summary.
11. Chedid V, et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Glob Adv Health Med. 2014;3(3):16-24. doi:10.7453/gahmj.2014.019 Our study summary.
12. Force M, et al. Inhibition of enteric parasites by emulsified oil of oregano in vivo. Phytother Res. 2000;14(3):213-4. doi:10.1002/(sici)1099-1573(200005)14:3<213::aid-ptr583>3.0.co;2-u Our study summary.
13. Akhtar MS, et al. Field trial of Saussurea lappa roots against nematodes and Nigella sativa seeds against cestodes in children. J Pak Med Assoc. 1991;41(8):185-7. https://pubmed.ncbi.nlm.nih.gov/1942479/
14. Boyko O, et al. Anthelmintic Activity of Traditional Medicinal Plants Used in Europe. Biology (Basel). 2025;14(12). doi:10.3390/biology14121636
15. Yousefnejad H, et al. Nigella sativa powder for helicobacter pylori infected patients: a randomized, double-blinded, placebo-controlled clinical trial. BMC Complement Med Ther. 2023;23(1):123. doi:10.1186/s12906-023-03955-4
16. Benito M, et al. Labiatae allergy: systemic reactions due to ingestion of oregano and thyme. Ann Allergy Asthma Immunol. 1996;76(5):416-8. doi:10.1016/S1081-1206(10)63456-4 Our study summary.
17. Gaudin O, et al. Association Between Severe Acute Contact Dermatitis Due to Nigella sativa Oil and Epidermal Apoptosis. JAMA Dermatol. 2018;154(9):1062-1065. doi:10.1001/jamadermatol.2018.2120
18. Arslan E, et al. A case study report of acute renal failure associated with Nigella sativa in a diabetic patient. J Integr Med. 2013;11(1):64-6. doi:10.3736/jintegrmed2013010
19. Wang X, et al. Severe Thrombocytopenia Associated With Black Seed Oil and Evening Primrose Oil. Cureus. 2020;12(6):e8390. doi:10.7759/cureus.8390
20. Wang Z, et al. Potential herb-drug interaction risk of thymoquinone and phenytoin. Chem Biol Interact. 2022;353:109801. doi:10.1016/j.cbi.2022.109801
21. Dong RH, et al. Identification of CYP isoforms involved in the metabolism of thymol and carvacrol in human liver microsomes (HLMs). Pharmazie. 2012;67(12):1002-6. https://pubmed.ncbi.nlm.nih.gov/23346763/
22. Hannan MA, et al. Black Cumin (Nigella sativa L.): A Comprehensive Review on Phytochemistry, Health Benefits, Molecular Pharmacology, and Safety. Nutrients. 2021;13(6). doi:10.3390/nu13061784