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Metabolite DUI: Driving With a Measurable Controlled Substance

When police gather evidence for a driving under the influence charge (DUI), they look for the byproducts of the ingested substance called metabolites. Police must base DUI charges on evidence. Metabolites offer proof that the offender metabolized a certain amount of a given substance at a given time.

The accuracy of sobriety tests conducted with properly calibrated blood-alcohol concentration (BAC) instruments is well-established. These tests aren't perfect. But they're relatively accurate at determining your level of alcohol intoxication at the time of a traffic stop.

Alcohol is just one of the countless substances that can cause impairment. Others, such as marijuana, heroin, and even legal prescription painkillers, are more difficult to measure. Many of these drugs stay in the system much longer than alcohol — long after they stop causing impairment. This challenges police officers to determine accurate impairment levels at a precise time.

This article discusses drug-related DUIs and metabolites. It also addresses driving under the influence of marijuana. Finally, it discusses state approaches to measuring controlled substance use by drivers.

Drug-Related DUIs and Metabolites

Breathalyzer tests don't directly measure the amount of alcohol in your bloodstream. Instead, they measure the concentration of the metabolites alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Your body metabolizes alcohol at a relatively fast rate of roughly .016 percent (or one average alcoholic drink) per hour. As a result, this measurement gives a reasonably accurate snapshot of a driver's BAC during a motor vehicle traffic stop.

This is not the case for legal or illegal drugs, which break down into their own unique metabolites. There are ways to detect and accurately measure those metabolites. As a result, many states have a "zero tolerance" or per se approach to non-alcohol DUI charges. This means a motorist who isn't impaired at the time of a traffic stop may still be guilty of driving under the influence of drugs. This is if the metabolites (either above a certain level or any detectable level, depending on state law) are present at the time of the stop.

Driving Under the Influence of Marijuana

Marijuana, also known as cannabis, is the most widely used recreational drug in the U.S. besides alcohol. It is perhaps the most challenging drug use to measure in the context of a DUI investigation. Many states will arrest DUI suspects who have any measurable level of THC (the psychoactive component of marijuana) in their blood. Lawmakers in states that have legalized the recreational or medical use of the herb are struggling to curb "stoned driving." But they also must respect the rights of their residents.

Complicating this is that marijuana metabolites remain in the bloodstream (as measured in urine) for roughly one week after ingestion. This is the case even though the high from marijuana may only last a few hours. This means the presence of marijuana metabolites in a urinalysis needs supporting evidence from a drug recognition expert. That evidence could consist of behavior such as:

  • Erratic lane changes
  • Bloodshot eyes
  • Slowed speech

The legal use of medical marijuana is no defense against DUI charges if the use causes impairment or if the state has a per se DUI law.

State Approaches to Measuring Controlled Substance Use by Motorists

As mentioned above, some states take a zero-tolerance approach to impaired driving. Regardless of the impairment of the driver at the time of a stop. That law means any detectable drug metabolite revealed through urine or blood screening can result in a DUI charge. Typically, there is other evidence of impairment. Blood draws are much less common, given how intrusive they are. State courts differ in how police may compel a blood draw after a DUI arrest.

The list of states with zero-tolerance drugged driving laws includes (but is not limited to) Iowa, Georgia, Arizona, and Michigan. Other states have a more nuanced approach to the assessment of drug impairment. Often, there are per se limits for certain drugs. These states include (but aren't limited to) the following:

  • Nevada — Per se impairment levels of 2 nanograms per milliliter of marijuana or 5 nanograms per milliliter of marijuana metabolite in a driver's blood only apply when the violation is punishable as a felony
  • Pennsylvania — Per se impairment for THC above 1 nanogram, any detectable level of other drugs (marijuana is illegal in the state)
  • Montana — Per se impairment if the government has a blood test that shows a whole blood content of 5 nanograms per milliliter or more of active THC

Many states, including California, have two separate charges related to DUI. One charge is for having a BAC higher than 0.08 percent, and the other pertains to other evidence of impairment. That means police can charge you with a DUI in California for:

  • Showing clear signs of impairment (regardless of BAC or metabolite content)
  • Having a BAC higher than 0.08 percent (or a detectable amount of drugs)
  • Showing clear signs of impairment and having a BAC higher than 0.09 percent

There's no immediate breath test for drugs other than alcohol. But law enforcement officers can use either blood or urine to screen for most drugs.

Contact a Lawyer About Your Driving Under the Influence Charge

Suppose you're driving while exceeding a certain level of drug metabolites. In that case, police can file a drunk driving or DUI charge against you regardless of actual impairment. Get professional help today from an experienced DUI lawyer. A criminal defense attorney can walk you through your DUI case and help you craft a defense, whether dealing with a first offense, misdemeanor, or felony. A defense lawyer can help assert affirmative defenses and help you avoid a lengthy driver's license suspension.

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