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DUI Laws Can Affect Marijuana Users, Too


In the past decade, marijuana laws have become significantly relaxed in many states across the country, with outright legalization for recreational use occurring in Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon, and Washington. Several other states, including our own (Maryland), have either decriminalized the drug, legalized it for medicinal purposes, or legalized small quantities for personal use.

Despite changing attitudes and laws concerning its usage, possession, and even cultivation, many users are finding themselves in legal trouble after consuming marijuana due to driving while impaired laws. And because marijuana legalization and decriminalization are relatively new, state legislatures and law enforcement agencies throughout the country are struggling to define what impaired driving looks like under the influence of marijuana and what the thresholds should be for fines, citations, and arrests.

How Does Law Enforcement Know When Drivers Are Impaired?

Police officers nationwide have long had a fairly standardized methodology for both pulling over drivers that they suspected are under the influence and arresting them after determining they are probably intoxicated. Those methods involved watching for irregular or erratic driving behaviors, evaluating drivers after pulling them over, and obtaining further evidence of intoxication via Breathalyzers or field sobriety tests.

But marijuana is different. There’s no easy way to tell if a driver is under the influence, and if he or she has consumed marijuana, it can be difficult to determine how much. When marijuana was illegal in all 50 states, police officers had easier times arresting people, which is ultimately what they want to do, because they could target the weed itself rather than the impairment from the weed. But now that the drug’s legal status has significantly changed, there has been a push for regulation of how much tetrahydrocannabinol (THC) is allowed in a driver’s system before he or she is over the legal limit. (

A few states have adopted measures to achieve that goal:

Five nanograms or more of THC per milliliter of blood – Colorado, Illinois, Montana, and Washington have all adopted this as the threshold for when drivers can be arrested for driving under the influence of cannabis.

Two nanograms or more of THC per milliliter of blood – Nevada and Ohio set a lower threshold for citations of driving under the influence of cannabis.

Experts say that as marijuana legalization continues to spread throughout the United States, other states will undoubtedly adopt similar platforms for determining whether drivers are too impaired to be behind the wheel after consuming cannabis. But science indicates that the levels may be arbitrary and may not necessarily correspond with similar thresholds for alcohol consumption, including the ubiquitous 0.08 blood alcohol content that all states use when pressing charges for DUI offenses.

An associate professor at Johns Hopkins University says that because alcohol is emitted via a person’s breath, it’s much easier to accurately determine levels of intoxication and impairment. But the quantities and impairment levels from other drugs, including marijuana, aren’t as easily measured. And when they are measured, they may not be reliable, as different concentrations of the active ingredients found in drugs like cannabis can affect people differently.

For example, long-term marijuana users are known to build up a tolerance to the effects of THC. That means a long-term user with five nanograms of THC per milliliter of blood may experience little to no impairment, while a relatively new or occasional user may experience profound impairment. In addition, a study by the AAA Foundation for Traffic Safety found that there was no significant correlation between blood concentrations of THC, driver impairment, and increased crash risks.

Because of the results of that study, the American Automobile Association and the National Safety Council both recommend that states don’t enact impaired driving laws based on THC levels found in drivers’ blood. Another problem that compounds the issue is the fact that THC levels rapidly drop in users’ bloodstreams, with levels being reduced by half within 20 minutes of a person’s last exposure to cannabis.

What Does the Future of Impaired Driving Detection Look Like?

Because of the unreliability of blood tests and the delays associated with administering them, law enforcement officers are looking for new, faster, and more effective ways to determine levels of cannabis intoxication in drivers.

A recent discovery by scientists at the National Institute of Standards and Technology in Boulder, Colorado, could create the potential to manufacture accurate marijuana breathalyzers. The devices would work by measuring the vapor pressure of THC that’s emitted in a user’s breath, which could then be used to determine the levels of THC in his or her blood.

The first marijuana breathalyzer is schedule to launch in 2018 with a retail cost similar to alcohol breathalyzers. And while the manufacturer of the device say its accurate for determining whether someone has THC in their system, they indicate that it can’t detect their precise level of intoxication, making it difficult for police to determine if drivers are dangers to themselves or others.

THC Impairment Laws Can Vary, But the Need for Legal Representation Doesn’t

Government officials in both Washington and Colorado have noted that traffic safety and crash statistics haven’t been affected by the legalization of marijuana. Despite that, law enforcement officers and agencies are still citing and arresting drivers who appear to be or are under the influence of marijuana.

As more states pass legalization or decriminalization statutes concerning marijuana, more police officers, state troopers, and sheriff’s deputies will be on the lookout for drivers who may be above the legal limit for marijuana consumption, despite the results of testing being inconsistent and inaccurate.

This leads to a difficult situation for drivers who get pulled over and charged with impaired driving or driving under the influence of cannabis, as the standards can vary from state to state and the effects of different bloodstream levels of THC can vary from person to person.

Having an experienced Maryland DUI lawyer on your side can help you protect your rights in such a confusing and subjective legal situation. At Shapiro Zwanetz & Lake, we know that people aren’t always treated fairly by the law—especially when the law is based on dubious or discredited science.

If you or someone you know was pulled over and cited or arrested for driving under the influence of cannabis, we’re here to help. Contact us today at (410) 927-5137 or submit a Free Consultation Form to get in touch with our legal team.