Consulting the doctor, verifying the source, verifying/checking on claims made, not exceeding the dosage are some basic precautions to be taken while using natural medicines. Seek and trust the evidence instead of testimonials or headlines.
One of the most common natural remedies used for hepatitis C is milk thistle (Silybum Marianum), found in most supplements which promote liver health. Its curative/medicinal power is believed to come from Silymarin, a group of flavanoids, with silybin as the key.
Not much is proven about the powers of milk thistle though. There is little research to show that use of its extract can cure hepatitis C. Poor absorption, lack of standardization, uncertainties about the source (most of the available milk thistle extract is from Chinese suppliers) are a few of the other concerns. Though it may not cause harm to the liver (unless one has hemochromatosis), avoid if you are pregnant, breastfeeding, or have a history of cancer which is hormone related.
For a detailed list of herbs considered unsafe for people with hepatitis C or liver diseases, a reference may be made to the hepatitis C Resource Center of U.S. Department of Veterans Affairs.