Dried oregano might not contain that much oregano leaves.
A study published in Which? found that 19 out of 78 samples of dried oregano contained other ingredients — mostly olive and myrtle leaves. These samples only had less than a third of oregano. Chris Elliott, director of the Global Institute for Food Security, noted that some dried oregano samples were made up of 30 to 70 percent olive and myrtle leaves.
These oregano samples were tested from stores in the United Kingdom and Ireland. Elliott said in the study, “Clearly we have identified a major problem and it may well reflect issues with other herbs and spices that enter the British Isles through complex supply chains. Much better controls are needed to protect the consumer from purchasing heavily contaminated products.”