title: Systematic review and meta-analysis of cannabis treatment for chronic pain.
abstract: METHODS
  Cannabis preparations have been used as a remedy for thousands of years in traditional medicine. Clinical use of cannabinoid substances is restricted, due to legal and ethical reasons, as well as limited evidence showing benefits.
  
  
  OBJECTIVE
  To assess the efficacy and harms of cannabis preparations in the treatment of chronic pain.
  
  
  METHODS
  Systematic review and meta-analysis of double-blind randomized controlled trials that compared any cannabis preparation to placebo among subjects with chronic pain. An electronic search was made in Medline/Pubmed, Embase, and The Cochrane Controlled Trials Register (TRIALS CENTRAL) of all literature published until February 2008, as well as specific web pages devoted to cannabis. Studies were cross-checked, selected, and assessed.
  
  
  RESULTS
  Eighteen trials were included. The efficacy analysis (visual analog scales) displayed a difference in standardized means in favor of the cannabis arm of -0.61 (-0.84 to -0.37), with statistical homogeneity (I(2) = 0.0%; P = 0.50). For the analysis of harms, the following Odds Ratios (OR) and number needed to harm (NNH) were obtained: for events linked to alterations to perception, OR: 4.51 (3.05-6.66), NNH: 7 (6-9); for events affecting motor function, 3.93 (2.83-5.47), NNH: 5 (4-6); for events that altered cognitive function, 4.46 (2.37-8.37), NNH: 8 (6-12).
  
  
  CONCLUSIONS
  Currently available evidence suggests that cannabis treatment is moderately efficacious for treatment of chronic pain, but beneficial effects may be partially (or completely) offset by potentially serious harms. More evidence from larger, well-designed trials is needed to clarify the true balance of benefits to harms.
authors.affiliation: Department of Clinical Research, Castile-La Mancha Health Research Foundation (FISCAM), Toledo, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Martín-Sánchez
authors.forename: Toshiaki A
authors.initials: TA
authors.lastname: Furukawa
authors.forename: Julian
authors.initials: J
authors.lastname: Taylor
authors.forename: Jose Luis R
authors.initials: JL
authors.lastname: Martin
mesh_terms: D000700:Analgesics / Q000008:administration & dosage* / Q000009:adverse effects; D002186:Cannabinoids / Q000008:administration & dosage* / Q000009:adverse effects; D002188:Cannabis / Q000009:adverse effects / Q000737:chemistry*; D002908:Chronic Disease / Q000188:drug therapy; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D006801:Humans; D010148:Intractable Pain / Q000188:drug therapy* / Q000503:physiopathology; D008517:Phytotherapy / Q000009:adverse effects / Q000706:statistics & numerical data*; D043882:Receptors, Cannabinoid / Q000187:drug effects / Q000378:metabolism; D018570:Risk Assessment; D016896:Treatment Outcome
chemical_list: D000700:Analgesics; D002186:Cannabinoids; D043882:Receptors, Cannabinoid