If the concentration of tetrahydrocannabinol (THC) in a person's whole blood is 5 nanograms or more, they are presumed to be under the influence of marijuana. This new law states that a jury can consider a person legally under the influence of marijuana if a blood test reveals the presence of 5 nanograms of THC per milliliter in that person's bloodstream. However, the limits per have been criticized for their potential to incriminate drivers who are not disabled, since THC can persist for long periods of time in a consumer. Overall, the presence of detectable THC in the blood suggests, but does not conclusively prove, that a person has recently used cannabis.
Since this THC in the blood can come from both a previous use and a recent use, it is not possible to differentiate between the two or to infer an alteration. While alcohol concentration (BAC or BrAc) is an accurate measure of alcohol deficiency while driving, the presence of THC in the driver's body has not been shown to be a reliable measure of marijuana driving impairment. In a study that monitored blood levels of THC in 25 chronic users, only nine of them did not consume measurable THC for a seven-day period without consuming the drug. The plant matter in smokable marijuana can range from 8 to 30 percent THC, while high-quality hashish oil could reach up to 80 percent THC.
The maximum THC level can occur when the deficiency is low, and the high deficiency can be measured when the THC level is low. The laws of states with specific marijuana laws are based solely on the amount of THC or a metabolite in a person's bloodstream. There is some evidence that higher levels of THC in the blood are associated with the driver's guilt in an accident. However, according to research by the AAA Foundation for Road Safety, there is no scientific evidence that a specific level of THC (delta-9-tetrahydrocannabinol, the main mind-altering component found in marijuana) in a person's bloodstream is associated with an alteration in the ability to drive.
THC then stays in adipose tissue for a long time, but small amounts slowly seep out of the adipose tissue and return to the blood over time, causing a continuous low blood concentration. Concentrate levels for steam ingestion are usually higher, as for edibles, although the rate of distribution in the blood varies considerably. Over time, other metabolites of THC were found to be better indicators of recent use and, according to some, of its deterioration.