title: Developing limits for driving under cannabis.
abstract: OBJECTIVE
  Development of a rational and enforceable basis for controlling the impact of cannabis use on traffic safety.
  
  
  METHODS
  An international working group of experts on issues related to drug use and traffic safety evaluated evidence from experimental and epidemiological research and discussed potential approaches to developing per se limits for cannabis.
  
  
  RESULTS
  In analogy to alcohol, finite (non-zero) per se limits for delta-9-tetrahydrocannabinol (THC) in blood appear to be the most effective approach to separating drivers who are impaired by cannabis use from those who are no longer under the influence. Limited epidemiological studies indicate that serum concentrations of THC below 10 ng/ml are not associated with an elevated accident risk. A comparison of meta-analyses of experimental studies on the impairment of driving-relevant skills by alcohol or cannabis suggests that a THC concentration in the serum of 7-10 ng/ml is correlated with an impairment comparable to that caused by a blood alcohol concentration (BAC) of 0.05%. Thus, a suitable numerical limit for THC in serum may fall in that range.
  
  
  CONCLUSIONS
  This analysis offers an empirical basis for a per se limit for THC that allows identification of drivers impaired by cannabis. The limited epidemiological data render this limit preliminary.
authors.affiliation: Nova-Institut, Hürth, Germany. franjo.grotenhermen@nova-institut.de
authors.forename: Franjo
authors.initials: F
authors.lastname: Grotenhermen
authors.forename: Gero
authors.initials: G
authors.lastname: Leson
authors.forename: Günter
authors.initials: G
authors.lastname: Berghaus
authors.forename: Olaf H
authors.initials: OH
authors.lastname: Drummer
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Krüger
authors.forename: Marie
authors.initials: M
authors.lastname: Longo
authors.forename: Herbert
authors.initials: H
authors.lastname: Moskowitz
authors.forename: Bud
authors.initials: B
authors.lastname: Perrine
authors.forename: Johannes G
authors.initials: JG
authors.lastname: Ramaekers
authors.forename: Alison
authors.initials: A
authors.lastname: Smiley
authors.forename: Rob
authors.initials: R
authors.lastname: Tunbridge
mesh_terms: D000063:Accidents, Traffic / Q000517:prevention & control*; D001334:Automobile Driving / Q000331:legislation & jurisprudence*; D002188:Cannabis / Q000009:adverse effects*; D016903:Drug Monitoring; D006801:Humans; D002189:Marijuana Abuse; D011596:Psychomotor Disorders; D012307:Risk Factors; D012309:Risk-Taking; D015813:Substance Abuse Detection / Q000331:legislation & jurisprudence / Q000379:methods*