Some herbs are deemed “toxic” or “slightly toxic,” but this usually implies long-term use. Long-term use can be widely interpreted, but most will agree that it constitutes drinking decoctions or taking powdered forms longer than one month.
Please feel free to list off some of the herbs you may understand (via research and/or clinical practice) to be safe and/or harmful for use (a) longer than one month, (b) longer than three months, and © longer than six months. Also when applicable, please reference your findings via providing a link(s).