Comfrey Tea Risks and Side Effects
and:
"Comfrey contains compounds that are toxic to the liver and animal experiments suggest it can cause liver cancer. "
I don’t buy that about comfrey. We had it there for the goats just outside the fence so they could nibble if they needed any. I’ve picked young leaves and dried them for tea. It’s been known for a long time to be beneficial for digestion.
Comfrey does technically contain toxins, but they are in tiny amounts, and it takes large doses over a long period of time before it starts to do any damage. So, unless you’re eating comfrey-leaf salads every day, you’re probably safe.
That said, if you already have liver problems, there’s a chance comfrey might aggravate them.
I generally reserve comfrey for things that are not ingested. It’s amazing on burns, and I make a tooth powder that’s half comfrey root, that works better than toothpaste.