Very poisonous. Sap contains cardiac glycosides which are steroid glycosides.

Sequin, M. (2012). The Chemistry of Plants. Perfumes Pigments and Poisons. Royal Society of Chemistry, Cambridge, UK. page137

"Humans/pets: TOXIC if eaten, smoke from burning is harmful."- HTA guidelines

The Horticultural Trades Association Guide to Potentially Harmful Plants 2022 https://hta.org.uk/poisonousplants