Julie Gardener
New Member
Researchers of the French National Institute for Transport and Safety Research (INRETS) and other French research institutions presented results of the largest ever conducted study on cannabis and driving in the British Medical Journal. The government funded study confirms results of earlier investigations that found no or only a small increase in the risk of causing an accident following the use of cannabis. The risk increased with increased THC blood concentrations as already observed in an Australian study published in 2004.
The case-control study included 10,748 drivers of different motor vehicles who were involved in fatal accidents in France between October 2001 to September 2003. Researchers compared the 6,766 drivers considered at fault in their crash (cases) with 3,006 drivers selected from the 3,982 other drivers (controls). 681 drivers had a THC blood concentration of above 1 ng/ml, of whom 42 per cent had also a blood alcohol concentration of above 0.05 per cent. 60.5 per cent of THC positive drivers were under the age of 25 compared to 24.5 per cent in the whole analyzed group of 9,772 drivers.
Detection of THC at any dose was associated with an increases risk of responsibility of 3.3. A THC blood concentration of below 1 ng/ml was associated with a responsibility rate of 2.2, which increased to 4.7 above a THC blood concentration of 5 ng/ml. If the additional presence of alcohol above 0.05 per cent was taken into account the risk for THC positive drivers decreased from 3.3 to 2.4 and if age of the drivers and other confounders were taken into account the risk further decreased to 1.8 for the THC positive group. After adjustment for all confounders a THC blood concentration below 1 ng/ml was associated with an increased risk of 1.6, which increased to 2.1 with a THC blood concentration above 5 ng/ml. Age below 25 was associated with an increased risk of 1.9. The adjusted risk for alcohol above 0.05 per cent in blood was 8.5. From their data researchers attributed 2.5 per cent of all fatal accidents to cannabis and 29 per cent to alcohol.
In a letter to the British Medical Journal Dr. Franjo Grotenhermen of the German nova-Institut wrote. "The presentation of the results in the abstract is somewhat misleading. The figures for the unadjusted odds ratios suggest a more than threefold risk increase for all THC positive drivers and a more than twofold increase even for drivers with a THC blood concentration of less than 1 ng/ml. However, closer review of the results shows that two other factors contributed to the higher accident risk, i.e., alcohol consumption and the younger age of the THC positive drivers, compared to the whole cohort. About 42 per cent of THC positive drivers also tested positive for alcohol, with a blood alcohol concentration (BAC) of 0.05 percent. Even an BAC below 0.05 per cent was reported to be associated with an odds ratio of 2.7 in the study, but no data were given on the percentage of THC positive drivers with an additional BAC < 0.05 per cent. Thus, no information is available on drivers who had only THC in their blood and on their risk of causing an accident, which has been used as a standard way of reporting in previous studies."
(Source: Laumon B, Gadegbeku B, Martin JL, Biecheler MB. Cannabis intoxication and fatal road crashes in France: population based case-control study. BMJ 2005 Dec 2 [electronic publication ahead of print])
Soruce: International Association for Cannabis as Medicine
The case-control study included 10,748 drivers of different motor vehicles who were involved in fatal accidents in France between October 2001 to September 2003. Researchers compared the 6,766 drivers considered at fault in their crash (cases) with 3,006 drivers selected from the 3,982 other drivers (controls). 681 drivers had a THC blood concentration of above 1 ng/ml, of whom 42 per cent had also a blood alcohol concentration of above 0.05 per cent. 60.5 per cent of THC positive drivers were under the age of 25 compared to 24.5 per cent in the whole analyzed group of 9,772 drivers.
Detection of THC at any dose was associated with an increases risk of responsibility of 3.3. A THC blood concentration of below 1 ng/ml was associated with a responsibility rate of 2.2, which increased to 4.7 above a THC blood concentration of 5 ng/ml. If the additional presence of alcohol above 0.05 per cent was taken into account the risk for THC positive drivers decreased from 3.3 to 2.4 and if age of the drivers and other confounders were taken into account the risk further decreased to 1.8 for the THC positive group. After adjustment for all confounders a THC blood concentration below 1 ng/ml was associated with an increased risk of 1.6, which increased to 2.1 with a THC blood concentration above 5 ng/ml. Age below 25 was associated with an increased risk of 1.9. The adjusted risk for alcohol above 0.05 per cent in blood was 8.5. From their data researchers attributed 2.5 per cent of all fatal accidents to cannabis and 29 per cent to alcohol.
In a letter to the British Medical Journal Dr. Franjo Grotenhermen of the German nova-Institut wrote. "The presentation of the results in the abstract is somewhat misleading. The figures for the unadjusted odds ratios suggest a more than threefold risk increase for all THC positive drivers and a more than twofold increase even for drivers with a THC blood concentration of less than 1 ng/ml. However, closer review of the results shows that two other factors contributed to the higher accident risk, i.e., alcohol consumption and the younger age of the THC positive drivers, compared to the whole cohort. About 42 per cent of THC positive drivers also tested positive for alcohol, with a blood alcohol concentration (BAC) of 0.05 percent. Even an BAC below 0.05 per cent was reported to be associated with an odds ratio of 2.7 in the study, but no data were given on the percentage of THC positive drivers with an additional BAC < 0.05 per cent. Thus, no information is available on drivers who had only THC in their blood and on their risk of causing an accident, which has been used as a standard way of reporting in previous studies."
(Source: Laumon B, Gadegbeku B, Martin JL, Biecheler MB. Cannabis intoxication and fatal road crashes in France: population based case-control study. BMJ 2005 Dec 2 [electronic publication ahead of print])
Soruce: International Association for Cannabis as Medicine
