It is well known that alcohol is a leading cause of liver diseases such as cirrhosis. With your liver already weakened from Hepatitis C, it is important to create a healthy environment for healing. Avoiding drinking will help you maintain liver health.
Every substance you ingest, your liver will attempt to break down. For the health of your liver, you should refrain not only from illegal drug use, but reconsider taking many legal pharmaceuticals, such as painkillers, diet pills and sleep aids, that will also have a profoundly negative effect on your liver. Always speak with your doctor before you take something, even something as harmless sounding as a protein powder supplement- there could be an ingredient lurking in that list that could spell trouble for your liver.
Marijuana and tobacco products are very harmful, especially the additives found therein. Please avoid smoking.