St John's Wort

Or known as Hypericum perforatum, which I planted a couple of years ago and is thriving.

It produces a few chemical compounds which are harmful to animals especially sheep and it was used in traditional medicine but more recently as an antidepressant. It can upset the balance in the body and effectiveness of prescription/over the counter drugs with the main ones being contraceptives, heart meds, HIV, cancer and anticoagulants.