title: Cannabis, Cigarettes, and Their Co-Occurring Use: Disentangling Differences in Gray Matter Volume.
abstract: BACKGROUND
  Structural magnetic resonance imaging techniques are powerful tools for examining the effects of drug use on the brain. The nicotine and cannabis literature has demonstrated differences between nicotine cigarette smokers and cannabis users compared to controls in brain structure; however, less is known about the effects of co-occurring cannabis and tobacco use.
  
  
  METHODS
  We used voxel-based morphometry to examine gray matter volume differences between four groups: (1) cannabis-dependent individuals who do not smoke tobacco (Cs); (2) cannabis-dependent individuals who smoke tobacco (CTs); (3) cannabis-naïve, nicotine-dependent individuals who smoke tobacco (Ts); and (4) healthy controls (HCs). We also explored associations between gray matter volume and measures of cannabis and tobacco use.
  
  
  RESULTS
  A significant group effect was observed in the left putamen, thalamus, right precentral gyrus, and left cerebellum. Compared to HCs, the Cs, CTs, and Ts exhibited larger gray matter volumes in the left putamen. Cs also had larger gray matter volume than HCs in the right precentral gyrus. Cs and CTs exhibited smaller gray matter volume than HCs in the thalamus, and CTs and Ts had smaller left cerebellar gray matter volume than HCs.
  
  
  CONCLUSIONS
  This study extends previous research that independently examined the effects of cannabis or tobacco use on brain structure by including an examination of co-occurring cannabis and tobacco use, and provides evidence that cannabis and tobacco exposure are associated with alterations in brain regions associated with addiction.
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA (Drs Wetherill, Jagannathan, Childress, Rao, and Franklin, and Mr Hager). rweth@mail.med.upenn.edu.
authors.forename: Reagan R
authors.initials: RR
authors.lastname: Wetherill
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA (Drs Wetherill, Jagannathan, Childress, Rao, and Franklin, and Mr Hager).
authors.forename: Kanchana
authors.initials: K
authors.lastname: Jagannathan
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA (Drs Wetherill, Jagannathan, Childress, Rao, and Franklin, and Mr Hager).
authors.forename: Nathan
authors.initials: N
authors.lastname: Hager
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA (Drs Wetherill, Jagannathan, Childress, Rao, and Franklin, and Mr Hager).
authors.forename: Anna Rose
authors.initials: AR
authors.lastname: Childress
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA (Drs Wetherill, Jagannathan, Childress, Rao, and Franklin, and Mr Hager).
authors.forename: Hengyi
authors.initials: H
authors.lastname: Rao
authors.affiliation: University of Pennsylvania, Department of Psychiatry, Philadelphia, PA (Drs Wetherill, Jagannathan, Childress, Rao, and Franklin, and Mr Hager).
authors.forename: Teresa R
authors.initials: TR
authors.lastname: Franklin
mesh_terms: D000328:Adult; D001921:Brain / Q000473:pathology*; D002188:Cannabis; D005260:Female; D066128:Gray Matter; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D002189:Marijuana Abuse / Q000150:complications* / Q000473:pathology*; D009929:Organ Size; D012907:Smoking / Q000453:epidemiology / Q000473:pathology; D014029:Tobacco Use Disorder / Q000150:complications* / Q000473:pathology*
keywords: Cannabis; dependence; gray matter volume; nicotine; voxel-based morphometry