Last November, Florida became one of many states to allow the use of medical marijuana for certain people. While recreational use remains illegal in this state, marijuana is gradually becoming more accepted across the country. One thing supporters and opponents of legalization generally agree on is that driving while under the influence of marijuana should remain a crime.
But how do law enforcement officers determine whether or not a driver is impaired by marijuana use? There's no clear answer to that question.
When the drug being consumed is alcohol, the situation is much clearer. In all states, a blood alcohol level of .08 or above is considered legally impaired. Blood alcohol level (also called blood alcohol concentration, or BAC) is measured by a breathalyzer or through a blood or urine test.
There is no currently accepted threshold for marijuana use
But there is no similar threshold for marijuana use-at least not one most experts agree on. The problem is that traces of marijuana can remain in the blood long after use. So detecting marijuana in a person's blood doesn't really tell you much. Marijuana found in the blood is not necessarily a sign of impairment.
"That just tells you somebody has smoked," says Margaret Haney, a professor of neurobiology at the Columbia University Medical Center. "But you don't know if they smoked an hour ago or if they smoked a week before or two weeks before."
Still, in 2015 a Florida lawmaker sponsored legislation that would have established a legal standard for marijuana impairment. The bill would have considered a blood level of 5 nanograms of tetrahydrocannabinol (THC), the active ingredient in marijuana, as legally impaired. But studies have found conflicting results about whether this level of THC corresponds to impairment. And some have found that heavy users have little or no impairment at much higher levels.
A blood test is also inconvenient, as it must be done by a doctor, nurse, paramedic or other medical professional. Law enforcement would like to have a device that measures THC blood levels through a breath test. And some devices have been developed, but the practical use of them is likely years away.
Field sobriety tests are a flawed and unreliable answer
For now, law enforcement officers rely on field sobriety tests to determine impairment. Common field sobriety tests include the walk and turn, one-leg stand and horizontal gaze nystagmus. The problem with field sobriety tests is that they are subjective and unreliable. There are a number of factors unrelated to drug or alcohol use that could cause a person to "fail" one of the tests.
There is no legal requirement to take field sobriety tests in Florida, and we advise everyone to respectfully decline to take them if asked. That's because "failing" these tests can have serious consequences. You could be charged with DUI. If convicted, you could face jail time, hundreds or thousands of dollars in fines, revocation of your driver's license and mandatory DUI classes. And if you've previously been convicted of DUI, the penalties could be much more severe.
In time, technology and a legal standard may be developed to determine marijuana impairment. But the current laws are confusing - and cause potentially serious consequences for drivers.