In 2004, healthcare professionals warned against overindulgence in Pontefract cake after a 56-year-old woman was admitted to hospital following an overdose. The woman consumed about 200 grams (7.1 oz) daily, leading to dangerously low potassium levels and subsequent muscle failure.
https://en.wikipedia.org/wiki/Pontefract_cake
At that dosage, this "sweet" is one of those things that one needs to keep locked away if there are any kids/dogs in the house.
Sugary-sticky medicine flavoured stuff made from a poisonous plant. It's the sort of thing I'd expect from a country with absolutely no food culture like the US.
Not what most people call poisonous. Of course, we mix extracts of that root with the known poison, dihydrogen monoxide.