Comfrey Leaves

Hi does anyone here eat comfrey leaves regularly? They appear to be packed with protein.

i know it has been banned in the USA and a few other countries due to PZAs(although there is similar amount in spinach and a few other commonly consumed plants. Apparently due two studies said it caused tumours in rats when fed up to 33% of its diet in comfrey leaves. Even then only a small proportion of the rats got tumours.

It is still regularly used for training horses.