Progression of chronic hepatitis is highly variable among individuals, as the result of several host, viral and environmental factors. The latter have been extensively investigated in order to ameliorate hepatitis C outcome, particularly in difficult-to-treat patients. Over the last decade, several studies have shown that a combination of HCV infection and high levels of alcohol abuse results in synergistic acceleration of liver fibrogenesis. In addition, recent data indicate that light alcohol intake may also exacerbate fibrosis progression. It has also been suggested that cigarette smoking may enhance activity grade in patients with chronic hepatitis C, thereby increasing progression of fibrosis. This assumption mostly relies on epidemiological evidences in the absence of pathogenic studies. Finally, cannabis use is increasingly emerging as a novel co-morbidity in patients with chronic hepatitis C. Indeed, regular cannabis smoking is an independent predictor of both fibrosis and steatosis severity in infected patients. In addition, experimental studies have shown that cannabinoid CB1 receptors enhance liver fibrogenesis and steatogenesis by distinct mechanisms, therefore strongly supporting epidemiological findings. Altogether, patients should be informed of the deleterious impact of alcohol, tobacco and cannabis use and should be offered appropriate support to achieve abstinence.