Oregano: a kitchen herb with almost no human trials

A meta-analysis of 45 intervention studies of Mediterranean herbs and spices in type 2 diabetes searched for oregano, and oregano was not among the five that improved fasting glucose. Those five were cinnamon, turmeric, ginger, black cumin and saffron. The abstract does not show whether any oregano trial made it in at all. A scoping review of 142 clinical studies of herbs and spices at culinary doses found no relevant human research on oregano. For oregano as you use it in cooking, we found no trial that measured the effect of oregano on its own in people. On paper the dried herb is dense. UK tables list 36.8 mg of iron and 1597 mg of calcium per 3.5 oz (100 g) of dried ground oregano, against 7.43 mg and 323 mg in fresh. We have no portion weight for oregano, and a sprinkle is a small fraction of 100 g.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• According to a 2025 analysis of EU control-plan data, 48% of oregano samples tested in a European Commission coordinated control plan were suspected of adulteration, mostly with olive leaves. — Oregano samples collected in the EU coordinated control plan for herbs and spices Evidence C source
  48% of oregano samples suspected adulterated, mostly with olive leaves
• In the UK food composition tables, dried ground oregano has 36.8 mg iron, 1597 mg calcium and 42.5 g fiber per 3.5 oz (100 g), while fresh oregano has 7.43 mg iron, 323 mg calcium and 8.6 g fiber. — CoFID 2021 (Public Health England), Oregano dried ground (13-878) and Oregano fresh (13-891) Evidence E source
  Per 100 g dried vs fresh: iron 36.8 vs 7.43 mg; calcium 1597 vs 323 mg; AOAC fiber 42.5 vs 8.6 g

What your body absorbs

• In a 4-week double-blind randomized trial in 45 healthy non-smoking men, juice with 600 mg/day of oregano extract phenolics markedly raised urinary phenolic excretion but did not change blood lipids or lipid peroxidation. — Healthy non-smoking men drinking mango-orange juice with 0, 300 or 600 mg/day total phenolics from Origanum vulgare extract (n = 45) Evidence B source
  Phenolic excretion markedly increased at 600 mg/d; no change in serum lipids, lipid peroxidation or safety markers

What cooking and storage change

• In cooked turkey patties stored at 4 C for up to 9 days, adding 200 mg/kg oregano oil to the meat slowed fat oxidation compared with untreated meat. — Turkey breast and thigh meat patties, oregano oil added post-mortem or via feed, cooked and refrigerated 3-9 days Evidence D source
  Lipid oxidation significantly retarded (P<0.05) at all storage times

What it does to your health

• In a randomized crossover trial in 12 men with overweight, adding 6 g of a 13-spice blend including oregano to a high-fat, high-carbohydrate meal reduced a post-meal inflammatory signal (IL-1beta from stimulated immune cells) at 4 h. — Non-smoking men aged 40-65 with overweight or obesity and at least one CVD risk factor, single meals with 0, 2 or 6 g spice blend (n = 12) Evidence B source
  IL-1beta secretion from LPS-stimulated PBMCs reduced at 240 min with 6 g, not 2 g

Safety, limits and interactions

• In a one-month randomized phase I study, healthy adults taking 1 or 2 mg/kg/day of carvacrol, oregano's main aromatic compound, kept all blood and urine test values within normal ranges. — Healthy young adults randomized to carvacrol 1 or 2 mg/kg/day for one month Evidence B source
  Some parameters shifted but all remained within normal range
• A case report from Algeria described a 77-year-old woman on the anticoagulant acenocoumarol whose INR rose to 6.42 after a week of daily oregano tea, and settled after she stopped it. — One 77-year-old woman with atrial fibrillation on acenocoumarol for 8 years, one 6.8 fl oz (200 ml) cup of oregano infusion daily (n = 1) Evidence D source
  INR 6.42 (target 2-3), fell to 3.80 the next day after stopping
• A case report described three systemic allergic reactions to eating oregano and thyme in one patient, with cross-sensitivity across the mint (Lamiaceae) family. — One adult patient with allergy to Labiatae herbs and ten control patients (n = 1) Evidence D source
  Systemic reactions; specific IgE to all tested Labiatae herbs

Who this works differently for

• A case report described a 13-year-old boy who developed angioedema after chicken seasoned with oregano, confirmed by a positive oral food challenge, while his skin prick test to oregano was negative. — One 13-year-old boy allergic to sage, mint and oregano (Lamiaceae) (n = 1) Evidence D source
  Angioedema; oral challenge to oregano positive

What is still unknown

• A scoping review of 142 clinical studies of culinary doses of herbs and spices for metabolic syndrome found no relevant human research for oregano. — Clinical trials of culinary doses of herbs and spices in healthy people or those with metabolic syndrome (n = 142 studies) Evidence C source
  Zero relevant studies for oregano
• A meta-analysis of 45 interventional studies of Mediterranean herbs and spices in type 2 diabetes, which searched oregano, found fasting glucose improved only with cinnamon, turmeric, ginger, black cumin and saffron. — People with type 2 diabetes in interventional studies of 12 Mediterranean herbs and spices (n = 45 studies) Evidence B source
  Oregano not among herbs improving fasting glucose

The bottom line

What is in the jar may not be all oregano. In a European Commission coordinated control plan, 48% of oregano samples tested were suspected of adulteration, mostly with olive leaves. That figure is second hand, quoted by a 2025 study, and the number of samples is not given there. It is a question of authenticity, and the source describes no direct toxic risk. The human trials that exist used extracts or blends. In 45 healthy non-smoking men, juice with 600 mg a day of phenolics from an oregano extract for 4 weeks markedly raised phenolics in urine, with no significant change in blood lipids or markers of fat oxidation. In 12 men with overweight, adding 6 g of a 13-spice blend that included oregano to a high-fat meal lowered one inflammatory signal from stimulated immune cells at 4 hours. The 2 g dose showed no such reduction. Oregano's own share of that effect is unknown, and it was a secondary outcome. In cooked turkey patties, 200 mg/kg of oregano oil slowed fat oxidation over up to 9 days in the fridge, which concerns the meat's shelf life. If you take a coumarin anticoagulant, one case report is worth knowing. A 77-year-old Algerian woman on acenocoumarol reached an INR of 6.42, against a target of 2 to 3, after a week of one cup of oregano tea a day. It fell to 3.80 the day after she stopped. She was also drinking verbena, and this is a single case. Allergy to oregano exists and can cross over within the mint family. One adult had three systemic reactions to oregano and thyme. A 13-year-old boy developed angioedema after chicken seasoned with oregano, confirmed by an oral challenge, while his skin prick test was negative. In a one month phase I study, healthy adults taking 1 or 2 mg/kg a day of pure carvacrol, oregano's main aromatic compound, kept all blood and urine values within normal ranges. That study had no placebo, and its abstract gives no sample size. We found no data on oregano in pregnancy.

Sources

1. orgn-daily-r2-07 · market survey
   Maybe the most striking outcome of the exercise was that 48 % of the oregano samples analysed were suspicious of being adulterated, mostly with olive leaves.
   Current Research in Food Science, 2025 · checked 2026-09-28
2. orgn-daily-r2-08 · reference dataset
   Oregano, dried, ground | CoFID 13-878 | Iron 36.80 mg | Calcium 1597 mg | AOAC fibre 42.5 g; Oregano, fresh | CoFID 13-891 | Iron 7.43 mg | Calcium 323 mg | AOAC fibre 8.6 g
   CoFID 2021, Public Health England, codes 13-878 and 13-891 (Open Government Licence v3.0) · checked 2026-09-28
3. orgn-daily-r2-01 · randomized controlled trial
   The excretion of phenolic compounds was markedly increased in the higher phenolic group as compared to the placebo group, but no significant changes were observed in the safety parameters, serum lipids, or biomarkers of lipid peroxidation.
   J Agric Food Chem, 2006 · checked 2026-09-28
4. orgn-daily-r2-09 · food experiment
   Post-mortem addition of either oregano oil or alpha-tocopherol to the minced meat also retarded lipid oxidation in the prepared patties compared with controls
   Int J Food Sci Nutr, 2004 · checked 2026-09-28
5. orgn-daily-r2-02 · randomized crossover trial
   IL-1β secretion from LPS-stimulated PBMCs was significantly reduced (1314%) at 240 min after HFCM consumption containing 6 g, but not 2 g, of spice blend compared with 0 g spice blend.
   J Nutr, 2020 · checked 2026-09-28
6. orgn-daily-r2-03 · phase I trial
   all post-treatment measured parameters were within normal range.
   Drug Chem Toxicol, 2021 · checked 2026-09-28
7. orgn-daily-r2-04 · case report
   On September 6, 2023, during a routine check-up, the patient's INR was 6.42, and the PT was 17.9%.
   Ann Cardiol Angeiol (Paris), 2025 · checked 2026-09-28
8. orgn-daily-r2-05 · case report
   We describe three systemic allergic reactions caused by oregano and thyme in the same patient.
   Ann Allergy Asthma Immunol, 1996 · checked 2026-09-28
9. orgn-daily-r2-06 · case report
   It was recognized that the first trigger, chicken meat with cheddar cheese, included oregano (Origanum onites L.). OFC for oregano was positive.
   Iran J Allergy Asthma Immunol, 2018 · checked 2026-09-28
10. orgn-daily-r2-11 · scoping review
    No relevant research was found for cloves, mint, oregano, parsley or thyme.
    Nutrients, 2023 · checked 2026-09-28
11. orgn-daily-r2-12 · meta-analysis
    Our results showed that cinnamon, turmeric, ginger, black cumin, and saffron significantly improved the fasting glucose levels in T2DM subjects.
    Nutrients, 2024 · checked 2026-09-28