Comfrey, coltsfoot and borage – what is the actual human evidence for harm?

Comfrey, coltsfoot and borage have a long history of therapeutic use, but have been implicated in safety issues due to the presence of unsaturated pyrrolizidine alkaloids (PAs). Consequently, a range of regulatory restrictions on their use have been put in place in many places where these plants are used. The review conducted by this research team examined both published case reports as well as data from the WHO adverse events database, and demonstrated that there are multiple factors which cloud the understanding around the human safety of these three medicinal plants.