Driving under the influence of drugs, including marijuana, is illegal. Yet while driving under the influence of alcohol can be established by measuring blood alcohol content, proving that someone is driving under the influence of marijuana is a bit more challenging.
Driving under the influence (DUI) of drugs is often referred to as a DUID. To be convicted of driving under the influence of marijuana, legal authorities must show that a suspect’s driving was impaired due to the presence of marijuana’s active ingredient, THC. Impairment can be defined as the inability to drive safely. Being under the influence of marijuana while driving may impair a driver’s ability to react to traffic conditions in a timely fashion.
Measuring the Influence of Marijuana
A police officer may detain any driver who seems to be driving unsafely. The police officer may also administer a field sobriety test to determine whether a driver is physically or mentally impaired. The symptoms of driving under the influence of drugs can be different than impairment due to excessive consumption of alcohol. Evidence gathered by any officer who has not been trained to recognize symptoms associated with marijuana impairment may be inadmissible in court.
When a driver is arrested for a drug-related DUI, a blood or urine test will typically be administered to detect the presence of drugs. In most jurisdictions, there is no legally defined amount of THC that can be in a driver’s system. Though authorities are able to detect the presence of inactive THC metabolites in urine, this cannot prove that a suspect was under the influence of THC at the time of the test. Inactive metabolites often remain in the body for extensive periods of time, depending upon how often someone uses marijuana.
Though blood tests are seldom used by authorities, a blood test may be capable of detecting active metabolites. At high levels, active metabolites are an indication that the THC was psychoactive when the blood test was administered. A blood test may also indicate the presence of low levels of active metabolites for as many as three days. There is a movement to adopt per se THC limits similar to the .08 blood alcohol standard. It is claimed that meta-analysis of experimental accident studies indicates that a per se limit of five nanograms of THC per milliliter of whole blood causes the same degree of impairment as.08 of alcohol.
Opponents of a per se THC limit complain that per se standards are unscientific and arbitrary. The National Highway Safety Administration (NHST) has notified law enforcement officials that urine test results cannot accurately predict impairment. Moreover, blood test results are only slightly more accurate. It is difficult for a prosecutor to prove that a driver was impaired by marijuana. In many jurisdictions, the prosecutor must prove that the capacity of a suspect to operate a vehicle was impaired to an appreciable degree.