Nobody has tested oil of oregano capsules or drops on a cold
The softgels and drops sold for colds have never been tried in people with one. The only oregano trial in a review of herbal cold and sinus treatments was a nasal spray for chronic sinusitis.
What the study found
No trial has tested swallowed oil of oregano against a cold
The capsules and drops sold for colds have never been tried in people with one, against placebo or anything else. A review of 47 herbal trials for colds and sinus conditions held a single oregano trial, a nasal spray for chronic sinusitis. The cold claim is untested, not disproven.
The caveat · A small-journal trial may be missed
The US trial registry lists 19 studies of oregano and none for a cold, so no cold trial is registered either. The one oregano trial that did turn up was published outside the main medical indexes, so a small trial published the same way could have been missed.