Herbs Contraindicated in Liver Disease

There is much posted and NOT posted about herbal remedies that are good or not good for the liver, especially concerning hepatitis C sufferers. Please do you have any information either way concerning the following: valerian, asafoetida, hops, gentian, mistletoe, margosa oil, mate tea, pennyroyal, chaparral, comfrey, skullcap. I've been told they are bad for hepatitis sufferers but no information why.

There is little real evidence that herbs cause liver damage due to lack of intensive studies. Reports of toxicity usually come from isolated cases, sometimes where the patient has overdosed on a herb. In some cases, there may be an isolated constituent that alone could cause damage, but together with its fellow constituents in the whole plant, there is minimal chance of harmful effects. In most cases, the constituent or mechanism of the herb causing damage is unknown. However, If I had a liver disease, I would stay clear of any herb that had reported damage.
Chaparral and comfrey have been banned in some countries due to reports of toxicity. In comfrey, the constituent pyrrolizidine alkaloids are considered toxic. Other herbs from your list that I know have been reported as possibly causing liver damage are: mistletoe, margosa oil, mate tea pennyroyal, skullcap.
Herbs that are particularly recommended for Hepatitis C are Milk Thistle, Dandelion, Artichoke, Licorice and Burdock.