I checked 6 pages of Google search results for "don't mix herbs." I found lots of warnings about mixing herbs and drugs. I also found a few, very few, pages that warned about mixing herbs with other herbs. The problem is, it was a general warning and no specific herbs were mentioned. Of course, that doesn't mean that we should be stupid when mixing herbs. We should always know what the herb does and learn as much as possible about anything we ingest, including what not to ingest with it.