Is there any research out there about the effects of smoking marijuana in people who do not smoke cigarettes?

Mixed results: The research in this area is mixed. Marijuana smoke contains more carcinogens than tobacco smoke. For instance, some studies show an increase in head & neck cancers in marijuana smokers: http://www.Ncbi.Nlm.Nih.Gov/pubmed/10613339 other studies suggest that smoking only marijuana does not lead to as many respiratory symptoms as smoking tobacco: http://www.Ncbi.Nlm.Nih.Gov/pubmed/19364790.