Cannabis produces dose-related impairments in a wide range of behavioural and cognitive functions. These include slowing reaction time and information processing, and impairing perceptual and motor performance, tracking behaviour and time perception. This is a scientific way of telling you that you are likely to feel a little sleepy and relaxed if you use cannabis! These effects can increase with the dose of THC and are larger and more persistent with tasks that require sustained attention. These effects may also have implications for accidents if the users drive or operate machinery while intoxicated. Laboratory driving simulator and standardised road studies have found impairments in driving skills after cannabis use, similar to those effects when blood alcohol levels are between 0.07% and 0.10%. However, more realistic on-road and simulator studies have found that cannabis drivers tend to be more cautious and drive more slowly, compared to alcohol-intoxicated drivers. So the research remains unfinished. This may be because smokers are aware of their intoxication and take appropriate precautions. Epidemiological evidence for the role of cannabis in road accidents is not conclusive. UK studies have found traces of illicit drugs in 18% of those killed in fatal accidents, with cannabis constituting around two-thirds of the drugs found. However, because traces of cannabis can remain in the body system for up to twenty-eight days the presence of cannabinoids in the blood of accident victims cannot be taken to indicate that the driver was intoxicated at the time of the accident. Many drivers in accidents also have a high blood alcohol level at the time of their accident.
