The trend is clear: States are legalizing the recreational or medical use of marijuana. In fact, twenty-three states plus the District of Columbia have legalized the use of marijuana in some form. Yet most state laws have not established clear methods or guidelines to assist law enforcement when they suspect a driver is under the influence of marijuana. It is easy enough for law enforcement to run chemical test for drivers suspected of driving under the influence of alcohol, but what chemical test can the officer employ if he or she suspects the driver is high on pot. Beyond that, is there even a legal amount of THC (the principal active component of marijuana) that the state allows while driving? Measuring driving impairment due to the influence of marijuana is not quite as easy to determine as alcohol impairment. Unlike alcohol, THC is not easily measured in the field and to complicate things, it can remain in the body long after its effects have worn off.

Methods for detecting and arresting someone for driving under the influence of marijuana are not only technically problematic but implicate individual due process rights. There are presently only two reliable methods for testing whether someone has recently used marijuana: blood and urine testing. The presence of THC in urine is not a reliable indicator of driving impairment since THC can remain in the urine long after its effects have worn off. A blood test can detect elevated concentrations of THC that may be consistent with recent use; however, such tests are a reliable indicator of recent use only within the first hour or so of that use. When a law enforcement officer suspects someone is driving under the influence of marijuana, they cannot perform a blood test on the spot; rather, they must transport the driver to a location where a tech can draw blood. By time this is accomplished, it isd quite likely that the THC levels in the blood have decreased considerably.

Currently several states have laws that prohibit a driver from having any detectable amounts of THC in their system; this is problematic and is certainly begging to be challenged in the upper courts as the mere presence of THC does not indicate impairment. Two states (Washington and Montana) have established a per se limit of THC that may be in a drivers system with levels above that limit, without any other indication that the driver is impaired, as grounds for an arrest for driving under the influence. Again, a court challenge may soon be waiting in the wings.

Recently in the State of New York, a driver successfully challenged her arrest and charge for driving under the influence of marijuana. Not only had this driver admitted to the police that she had “smoked weed earlier,” but the officer noted her bloodshot glassy eyes, slurred speech and unsteady stance. Despite the driver’s admission, which is considered hearsay under New York law without corroboration, the court dismissed the complaint against the driver because the officer failed to corroborate her statement by stating in the arrest report that her appearance or demeanor was consistent with the use of marijuana or, as is often the case, that the officer smelled marijuana emanating from the vehicle or from the driver.

New York law does not make any statement regarding the presence of THC in the body in its DWI law; nor does California law. Similar to the laws in New York, California merely makes it illegal to drive under the influence of drugs. How that is established most often relies on the subjective evaluation of the officer and objective findings such as the smell of burnt marijuana or the presence of marijuana on the driver or in the vehicle.

The laws prohibiting marijuana use, whether recreationally or medicinally are rapidly falling away. How the states treat drivers under the influence of marijuana will certainly present challenges to law enforcement and the courts for years to come.


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