The previous three studies should be enough to indicate what’s going on with oregano. In humans and in the laboratory, oregano kills a wide range of microorganisms. The third study listed above demonstrates that the antiseptic properties of oregano can be profound, meaning the difference between life and death for the mice in that study.
This next study gets right to the heart of the matter. The study investigated the effect of a nasal spray consisting of several essential oils including oregano oil in 60 humans with upper respiratory tract infections (the sore throat and congested lung infections that often accompany a cold).
This study is of the highest calibre, as it is a randomized, double-blind, placebo-controlled trial. The patients were split into two groups, one group received the treatment while the other group received a placebo.
Neither the patients nor the doctors and nurses who interacted with them knew which patients received the treatment, and which did not. (The best medical studies are done this way so that the observations and results will reflect only the results of treatment, and will not be affected by biases that the doctors or patients may have for, or against, the treatment.) The statistical analysis showed that 20 minutes following the treatment, the patients who had received the treatment reported a greater improvement in symptom severity compared to participants in the placebo group. They describe their nasal spray as providing a “significant and immediate improvement in symptoms of upper respiratory ailment”.
Treatment of upper respiratory tract infections in primary care: a randomized study using aromatic herbs.
Ben-Arye E, Dudai N, Eini A, Torem M, Schiff E, Rakover Y.
Evid Based Complement Alternat Med., 2011, 690346.