Irinotecan

Yes, there are real case reports of toxicity, and similar drugs like everolimus are often used in cancer treatment.

Other drugs with similar interactions are doxorubicin, the whole Taxol family, the Tecan family, Irinotecan, Topotecan, and some of the tyrosine kinase inhibitors.

And also, the one that nobody really checks, berberine can prolong what we call the QT interval, or the space in between heartbeats, which is a heart rhythm risk.

If you stack berberine on top of cancer drugs that already do that, and many of them do...