a1 Section of Neuroimaging, PO67 Division of Psychological Medicine, Institute of Psychiatry, King's College London, UK
a2 Neuropsychopharmacology Group, IMIM-Hospital del Mar and Department of Psychiatry; Institute of Neurosciences, Hospital Clinic, IDIBAPS, CIBERSAM, Barcelona, Spain
a3 INCT Translational Medicine, Brazil
a4 Universidad Autónoma de Barcelona, Barcelona, Spain
a5 Department of Neurosciences and Behaviour, School of Medicine of Riberão Preto, São Paulo University, Brazil
a6 Psychiatric Out-patient Department (SJB), University Hospital Basel, Basel, Switzerland
a7 Melbourne Neuropsychiatry Centre, The University of Melbourne, Australia
a8 Department of Psychiatry, School of Medicine, Sao Paulo University, Brazil
Background We conducted a systematic review to assess the evidence for specific effects of cannabis on brain structure and function. The review focuses on the cognitive changes associated with acute and chronic use of the drug.
Method We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. The search was conducted using Medline, EMBASE, LILACS and PsycLIT indexing services using the following key words: cannabis, marijuana, delta-9-tetrahydrocannabinol, THC, cannabidiol, CBD, neuroimaging, brain imaging, computerized tomography, CT, magnetic resonance, MRI, single photon emission tomography, SPECT, functional magnetic resonance, fMRI, positron emission tomography, PET, diffusion tensor MRI, DTI-MRI, MRS and spectroscopy.
Results Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. The high degree of heterogeneity across studies precluded a meta-analysis. The functional studies suggest that resting global and prefrontal blood flow are lower in cannabis users than in controls. The results from the activation studies using a cognitive task are inconsistent because of the heterogeneity of the methods used. Studies of acute administration of THC or marijuana report increased resting activity and activation of the frontal and anterior cingulate cortex during cognitive tasks. Only three of the structural imaging studies found differences between users and controls.
Conclusions Functional neuroimaging studies suggest a modulation of global and prefrontal metabolism both during the resting state and after the administration of THC/marijuana cigarettes. Minimal evidence of major effects of cannabis on brain structure has been reported.
(Received October 17 2008)
(Revised June 05 2009)
(Accepted June 10 2009)
(Online publication July 23 2009)
c1 Address for correspondence: Dr R. Martín-Santos, Department of Psychiatry, Institute of Neurosciences, Hospital Clinic, IDIBAPS, CIBERSAM, Villarroel, 170, 08036 Barcelona, Spain. (Email: firstname.lastname@example.org)