Exposure to marijuana may have biologically-based physical, mental, behavioral, and social health consequences and is "associated with diseases of the liver (particularly with co-existing hepatitis C), lungs, heart, eyesight, and vasculature" according to a 2013 literature review by Gordon and colleagues. The association with these diseases has only been reported in cases where people have smoked cannabis. The authors cautioned that "evidence is needed, and further research should be considered, to prove causal associations of marijuana with many physical health conditions".