600 mg oregano oil extract was orally administered for 6-weeks to 14 patients who had tested positive for the intestinal parasites Blastocystis hominis, Entamoeba hartmanni and Endolimax nana. After the 6 week treatment there was complete disappearance of Entamoeba hartmanni in 4 cases, Endolimax nana in 1 case, and Blastocystis hominis in 8 cases. Gastrointestinal symptoms also improved in 7 of the 11 patients who had tested positive for Blastocystis hominis.
Oregano extract immobilized all of the furcocercariae (parasitic larva) of Schistosoma haematobium exposed to the extract within 15 min. Schistosoma haematobium are parasites found in the urinary bladder.
Mexican oregano (Lipia beriandieri) extract has been shown in vitro to be effective against the giardia parastite, and superior to tinidazol which is a drug of common use in the treatment of giardiasis.

The inhibitory effects of 10 selected Turkish spices, including oregano, towards growth of 9 food borne fungi were investigated. Of the spices tested, only oregano showed effect on all fungi. Oregano essential oil and it’s ingredients thymol and carvacrol at concentrations of 0.025% and 0.05% completely inhibited the growth of all fungi.
The oil of oregano is a potent inhibitor of yeast, including Candida albicans.

Some essential oils and their main constituents were evaluated in-vitro against a strain of Candida albicans. The essential oil of Origanum vulgare was one of 5 oils that showed maximum inhibitory activity against Candida albicans after 7 days.

The culinary herbs oregano, sage, peppermint, garden thyme, lemon balm, clove, allspice and cinnamon all contain very high concentrations of antioxidants and intake of herbs may contribute significantly to the total intake of plant antioxidants, and may be an even better source of dietary antioxidants than many other food groups such as fruits, berries, cereals and vegetables.