While California DUI attorney prosecutors maintain that alcohol makes one drive fast, marijuana use makes drivers more cognizant of the speed limit.
Less 5 ng in one's system is consistent with a claim that an individual had not smoked marijuana since the previous day.
Based on the research discussed below it is also indicative of ingestion occurring at least 3 hours prior to the test. As a result, this level would not be expected to cause impairment.
Marijuana has been shown to impair performance on driving simulator tasks and on open and closed driving courses for up to approximately 3 hours. After that period, most effects have returned to baseline levels. Even where impairment is present, however, evidence from studies strongly suggests that those using marijuana alone exercise greater caution when driving. As a result, even when impaired, some drivers actually improve their performance by overcompensating for self-perceived impairment.
Despite the possibility of impairment at higher doses, NHTSA sponsored studies have shown that low doses of marijuana taken alone, do not impair city driving performance and do not diminish visual search frequency for traffic at intersections. In fact, some studies have even reported improvement in driving performance in subjects at low doses of marijuana.
THC is the primary psychoactive constituent of marijuana. Most behavioral and physiological effects of THC return to baseline levels within three to six hours after exposure. This tracks with the concentration of THC in an individual’s system which declines rapidly and is often < 5 ng/ml three hours after use. Generally concentrations in the range of 7-29 ng/ml for THC in blood are necessary to induce even 50% of the maximal subjective high effect. Further, levels of THC in plasma over 25-30ng/ml are typically required before inducing failure on roadside sobriety tests. Thus, even when detectable, THC's adverse effects on driving performance have been determined to be relatively small.
As a result of the factors described above, it is difficult to establish a relationship between an individuals THC blood or serum concentration and any performance impairing effects it may have. Further, due to chemical and pharmacokinetic differences between marijuana and ethanol, we can not use ethanol as a model for relating drug concentrations to effects.
In fact, NHTSA sponsored studies have found that it is not possible to conclude anything about a driver's impairment on the basis of his/her plasma concentrations of THC determined in a single sample. Thus, one should not try to predict impairment based on blood THC concentrations alone.
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