The present invention is directed to methods and compositions employing 9-(4-hydroxy-2-(hydroxymethyl)butyl)guanine (“H2G”) or derivatives or analogs thereof for the treatment of viral diseases, as well as for the treatment of other conditions, including, but not limited to, cancer, chronic fatigue syndrome, Alzheimers disease, multiple sclerosis and Graves disease. The H2G or derivative or analog thereof can be administered in a pharmaceutical composition and can be administered with an additional antiviral therapeutic agent or another agent for the treatment of other conditions.