With recreational marijuana legal in 18 states, the need for laws determining whether someone is too stoned to drive has risen. However, it’s been a challenge for states to decide how to determine when someone is high and unable to drive without endangering public safety. Let’s look at the difficulties of deciding what too high is and how to recognize when you or someone else is too stoned for driving to be safe.

Signs of being under the influence of marijuana

Smoking or ingesting marijuana affects users in different ways, but there are a few signs you can look out for to spot someone who is too stoned to drive.

According to the Addiction Center, short-term signs include bloodshot eyes, anxiety or paranoia, cognitive impairment, impaired motor function, slowed reaction times, elevated heart rate, sleepiness, and overeating. However, frequent marijuana users might have difficulty standing on one leg even when not high.

Is driving under the influence of marijuana dangerous?

Regulations on drinking and driving have long been in place, but the law is still catching up with marijuana use and driving. There isn’t a Breathalyzer test for pot-smoking, and the signs of marijuana impairment are subjective.

Scientific studies have generally found that marijuana impairs a driver’s abilities by reducing focus and slowing reflexes. However, the impairment is similar to having a blood alcohol level between .01 and .05, which is within the legal limit, The Marshall Project reports.

Rune Elvik, a University of Oslo political scientist who has done multiple meta-analyses of the risks of drugged driving, compares the increased impairment to the heightened difficulty of driving in the dark instead of the daytime. However, the Insurance Institute for Highway Safety has found that states with legalized marijuana have higher rates of crashes.

Apps that can tell if someone is too stoned to drive

But how can you tell if you or someone else is too stoned to drive? Of course, there’s an app for that. According to Analytical Cannabis, one is Otorize. Another is Druid.

Though a blood or Breathalyzer test can tell if someone has a high blood/alcohol concentration after drinking, testing for cannabis impairment hasn’t been as simple as testing for THC levels. THC is tetrahydrocannabinol, the marijuana component responsible for making users high.

Police have relied on blood, urine, or saliva THC tests or on human judgment, The Daily Beast reports. Instead of checking THC levels, the apps check for cognitive impairment. These digital cognitive tests can help users judge their own impairment after using any controlled substance.

You can find Otorize in the Google Play Store and Druid in the Google Play Store and the App Store.

The difficulties of testing for marijuana impairment

Unlike alcohol, the impairment caused by marijuana use isn’t directly correlated with the amount used, the time period of use, or the concentration of the drug. This makes it difficult to define what being high from marijuana means.

THC levels spike quickly and can leave the bloodstream in under three hours even though the effects can remain for nine hours. People who use marijuana regularly might have THC in their blood for days or weeks even though they’re not stoned anymore. Tests don’t indicate when the marijuana was used. In addition, different people are affected differently.

Regardless of the difficulty in connecting THC levels to impairment levels, many states have legal limits for THC in the blood. Though some states make any level of THC in the blood illegal for driving, others set specific limits.

States have different laws regulating marijuana use and driving, but it continues to be difficult to tell if someone is too stoned to drive because marijuana affects people differently from the way alcohol does. Drivers can look for symptoms and use apps to help gauge whether they’re able to drive safely. But when in doubt, it’s best to let someone else drive.