J.C. Suris et al., “Some Go Without a Cigarette: Characteristics of Cannabis Users Who Have Never Smoked Tobacco,” Archives of Pediatric Adolescent Medicine 161, issue 11 (November 2007): 1042-1047.
This study examined differences between youth who use both tobacco and marijuana compared to youth who use marijuana only, and to youth using neither substance. The marijuana-only adolescents showed better functioning than those who also use tobacco. In most ways they were similar to the abstainers, did not seem to have psychosocial problems at a higher rate, had better peer relationships, were more involved in sports, and more likely to be on an academic (as opposed to vocational) track in school.
Abstract and full text available for free at: http://archpedi.ama-assn.org/content/vol161/issue11/index.dtl