Kaiser Study Links Marijuana and Accidents; Confirms Cal NORML’s Advice to Users

Kaiser Health researchers have published a study showing that marijuana use is correlated with a significant increase in the risk of hospitalization due to injuries. The study, published in the April 2003 edition of the Annals of Epidemiology, covered 64,657 subjects from Northern California, of whom 13,971 were current marijuana users. Researchers found that among men, current marijuana users had a 28% higher rate of hospitalization due to injuries than non-users; among women, the increase was 37%. Results were adjusted for alcohol and tobacco use, as well as age, race, education, marital status and medical conditions.

California NORML coordinator Dale Gieringer said that he was not surprised by the results. “This accords with what we have long been advising users in Cal NORML’s “Marijuana Health Myths and Facts”, namely that accidents are the number one health hazard from marijuana use. However, this hazard is not inordinate and can be reduced by exercising responsible judgment.”

In an analysis of different injury causes, the study found a significant increase in injuries due to motor vehicles in males (1.96 times higher in users than non-users); for females, the risk ratio (1.23) was not statistically significant. These results don’t necessarily reflect greater driving recklessness, since they include injuries to passengers, pedestrians and innocent drivers. Other driving studies have suggested that marijuana users are more likely to be injured in auto accidents, yet are no more likely than other drivers to be responsible for driving fatalities.

Curiously, men who used marijuana more frequently (>1x per week) had a lower injury rate than those who used it only occasionally (risk ratios 1.36 and 2.00 respectively). For women, risks increased with frequency of use. However, in the case of motor vehicle accidents, frequent use of marijuana (>1x per week) was associated with a greater than two-fold increase in injuries in both men and women (2.47 and 2.18 respectively).

The Kaiser study also found a significantly higher rate of injuries due to assaults in males (risk ratio 1.90), a result which is difficult to explain as due to marijuana impairment. Like other drug users, marijuana users are known to have a higher risk preference than the general population, and may therefore be more likely to find themselves in dangerous situations. In addition, of course, the illegality of marijuana may put users at a greater risk of robberies.

The study authors concluded, “although the results of this study must be viewed cautiously, it is suggested that marijuana use may be independently associated with increased risk of injury.”

California NORML notes that the inferred risk from marijuana is not inordinate compared to that of many other everyday products, including alcohol, tobacco, guns and automobiles. An abstract of the study follows below. Note that it erroneously states that the injury risk ratios for marijuana users were 1.58 for males and 1.55 for females adjusted for alcohol and tobacco use and other factors; actually, these were adjusted only for age; the fully adjusted ratios were 1.28 and 1.37. By way of comparison, cigarette smokers have an accident risk ratio of 1.51 compared to non-smokers; teen drivers have two to five times the accident risk of older drivers; and males are twice as likely as females to have auto crashes.

(Sources: R Lancaster & R Ward, “The contribution of individual factors to driving behaviour”, Entec UK Ltd 2002 http://www.hse.gov.uk/research/rrhtm/rr020.htm ;
Leisitkow et al, “Smoking as a Risk Factor for Accident Death” Accident Analysis & Prevention May 2000)

Release by Dale Gieringer, Cal NORML Apr 4 2003

Marijuana Use and Injury Events Resulting in Hospitalization

Ann Epidemiol 2003;13:230-237. © 2003 Elsevier Science Inc. All rights reserved.

PURPOSE: Information on the potential relation between marijuana use and the incidence of hospitalized injury is extremely limited. The purpose of this effort was to investigate the potential for this association.

METHODS: A retrospective study was conducted in a large prepaid Northern California health care program cohort (n 64,657) that completed baseline questionnaires about health behaviors, including marijuana use, and health status between 1979 and 1985. All injury hospitalizations through December 31, 1991 (n 965) were identified and validated.

RESULTS: Using Poisson regression modeling, increased rate-ratios and 95% confidence intervals were identified for all-cause injury hospitalizations for both men and women among current users (1.58; 1.29 to 1.94 and 1.55; 1.12 to 2.10, respectively) relative to nonusers, adjusted for age, cigarette and alcohol use, and other potential confounders [This is incorrect, these figures are only adjusted for age – DG]. Increased rates of motor vehicle (2.31, 1.44 to 3.72), assault (2.63, 1.56 to 4.46), and self-inflicted (3.43, 1.54 to 7.87) injuries were identified among men who were current users; an increased rate of self-inflicted injuries (2.13, 1.05 to 4.10) was also identified in women who were current users.

CONCLUSIONS: Though the results must be viewed cautiously, they suggest that marijuana use may be independently associated with increased risk of hospitalized injury. Further study of the physiological and behavioral mechanisms is warranted.

KEY WORDS: Marijuana Use and Injury, Motor Vehicle Injury, Assaults, Intentional Injury.