Oregano oil kills bacteria and fungi in the laboratory, but human evidence is far thinner: a few small studies, mostly without comparison groups, suggest it clears gut organisms. Against that sit burning and stomach upset, skin irritation when undiluted, laboratory signs it may speed liver drug clearance like St John's wort, and most tested products far below their claimed potency. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Ferritin | 50–150 ng/mL | Iron stores; carvacrol dosing lowered serum iron in the only formal safety trial |
| Serum iron and transferrin saturation | Transferrin saturation 25–35% | Detects the specific fall seen at 2 mg/kg/day carvacrol before ferritin moves |
| Haemoglobin and haematocrit | Haemoglobin 13.5–15.0 g/dL (men), 12.5–14.5 g/dL (women) | Red-cell count and haematocrit both declined during sustained carvacrol dosing |
| HDL cholesterol | Above 55 mg/dL (men), above 65 mg/dL (women) | The one lipid marker with directly conflicting evidence — up with whole oil, down with purified carvacrol |
| ALT and GGT | ALT below 20 U/L (men), below 17 U/L (women); GGT below 20 U/L | Screens for liver injury from concentrated botanical oils |
| hs-CRP | Below 0.5 mg/L | The inflammatory marker most likely to move if the anti-inflammatory signal is real |
| Lactulose or glucose breath test | Normalisation: no rise above 20 parts per million of hydrogen within 90 minutes | Defines whether bacterial overgrowth actually cleared |
| Stool pathogen and parasite panel | Negative result on repeat testing | The endpoint used in the parasite study, and the only objective proof of clearance |
| Narrow-therapeutic-index drug levels (tacrolimus, ciclosporin, phenytoin, clozapine) | Each drug's own established therapeutic window | Detects the enzyme induction predicted by laboratory data before clinical failure occurs |
Cadence: Baseline before starting; tolerability reviewed at one week; narrow-therapeutic-index drug levels at four weeks and again 2–4 weeks after stopping; confirmatory test, iron measures and lipids repeated at the end of the course; iron status and liver enzymes every 6–12 months if pulsed cycles continue.