Driving while under the influence of marijuana is dangerous and illegal. Marijuana use impairs cognitive function, motor skills, and judgement, which are all critical for operating a vehicle safely. While the effects vary by individual, no one should get behind the wheel while high.
What is marijuana impairment?
Marijuana contains THC, a psychoactive compound that causes intoxication. THC affects areas of the brain responsible for memory, pleasure, concentration, sensory and time perception, and coordinated movement. This impairsdriving skills in the following ways:
- Slower reaction time
- Reduced coordination and motor control
- Impaired judgement of speed and distance
- Decreased ability to pay attention and focus
- Problems with memory and decision making
These effects make it more difficult to safely operate a vehicle and respond to driving situations. Even small amounts of THC can alter perception and cognition. While some people may not feel very high, they can still be dangerously impaired.
Is driving high as dangerous as drunk driving?
Yes, driving under the influence of marijuana does increase accident risk similar to drunk driving. However, the effects of marijuana vary more between individuals than alcohol.
Alcohol is water soluble so it is quickly absorbed and distributed through the body. The levels can be reliably estimated by blood alcohol concentration. THC is fat soluble so the absorption and impairment is highly variable based on the dose, potency, method of use, and tolerance of the user.
While it’s hard to measure just how impaired someone is from marijuana, considerable evidence shows driving under the influence increases crash risk:
- Studies show that people who drive within a few hours of using marijuana are nearly twice as likely to be involved in a crash.
- Marijuana users have slower driving reaction times, impaired automatic driving abilities, and difficulty maintaining a steady position in the traffic lane.
- Fatal crashes involving drivers who test positive for marijuana have tripled over the past decade.
So while comparisons are difficult, marijuana definitely causes significant impairment. Drivers should treat marijuana similarly to alcohol and never operate a vehicle while impaired.
How long does marijuana stay in your system?
Marijuana can be detected in the body for weeks after last use, but impairment usually only lasts for a few hours. Here is how long it stays in your system:
- Impairment: The intoxicating effects of THC usually start within minutes after smoking and peak within 30 minutes. Effects can last up to 4 hours or longer with high doses.
- Blood: THC is rapidly absorbed into the bloodstream. It can be detected in the blood for up to 24 hours after last use.
- Saliva: Saliva tests can detect THC for up to 72 hours after use.
- Urine: Urine tests detect a marijuana metabolite called THC-COOH. This can be found in urine 3-30 days after use in regular users.
- Hair: THC and its metabolites can be detected in hair for months or years after use. A standard hair test can detect repetitive marijuana use over a 90 day period.
So while THC leaves the blood quickly, it lingers in other places. A positive drug test does not necessarily mean the person is currently impaired.
How long to wait before driving?
There is no set time for how long to wait before driving after using marijuana. Effects usually peak shortly after use. Some guidelines include:
- Smoking – 4 hours is a minimum, but impairment effects could last longer
- Vaping – 3 hours
- Edibles – 6-8 hours or longer due to slow absorption
- High doses can cause impairment for 12-24 hours
The safest option is to avoid driving for at least 24 hours after getting high. Since marijuana affects each person differently, you should never operate a vehicle if you feel impaired in any way.
Does marijuana increase crash risk?
Yes, many studies have found that using marijuana increases crash risk, especially fatal crashes:
- One study found that drivers who tested positive for THC were 25% more likely to be in a crash.
- In fatal crashes, marijuana users are three times more likely to be at fault.
- Analyzing decades of data showed states that legalized marijuana saw a 5.2% increase in crash rates.
- In one study, 6.8% of drivers in fatal crashes tested positive for THC, with or without alcohol.
The increased risk is highest among frequent marijuana users. People who use marijuana regularly, even daily, tend to develop some tolerance and may not feel very impaired. However, research shows their driving abilities are still significantly impaired compared to sober individuals.
Do marijuana laws affect traffic safety?
Studies on the impact of marijuana legalization show mixed effects on traffic safety:
- Some studies show an increased risk of fatal crashes in states after legalizing marijuana. For example, one study found a 2.5% higher rate of fatalities.
- Other analyses indicate legalization has not substantially changed overall traffic fatality rates.
- There are some signs that teen marijuana use and car accidents decline after legalization, perhaps because it is harder for teens to obtain marijuana once drug dealers are removed.
- However, surveys show that marijuana use before driving increases among adults after legalization.
The impact likely depends on specific policies. For example, setting marijuana taxes low enough to compete with the black market seems to increase use and impaired driving. More research is still needed as states gain experience with legalization.
What are the penalties for driving high?
All states have laws prohibiting driving under the influence of marijuana. Penalties are similar to drunk driving and typically involve:
- Jail time – Up to 1 year in jail for misdemeanor DUI charges. Felony charges can involve years of jail time.
- Fines – Around $1,000 for a first offense plus several thousand more in legal fees and increased insurance costs.
- License suspension – Usually 6 months to a year on a first offense.
- Probation – Terms often include random drug testing and substance abuse counseling.
- Ignition interlock – May be required to pass a breathalyzer test to operate your vehicle.
Penalties go up significantly for repeat offenses. Those caught driving high also face consequences beyond the criminal charges, like loss of job opportunities and damage to social relationships. The costs are simply not worth the risk.
How do police test for marijuana impairment?
Police have two ways to test for marijuana impairment when pulling over drivers:
Field sobriety tests – Standard field sobriety tests assessing balance and coordination can indicate impairment, but lack accuracy identifying it is from marijuana. Police officers receive advanced training to detect signs of marijuana intoxication during these tests.
Blood tests – The most definitive way to identify marijuana is to measure THC levels in the blood. However, because THC leaves the blood quickly, tests may underestimate impairment. Zero tolerance laws in some states make it illegal to drive with any detectable THC in the blood.
Urine or saliva tests are not valid ways to measure driving impairment, since THC can be detected days or weeks after use when no impairment exists. Breathalyzers for THC are being developed but are not yet in widespread use.
How common is driving high?
Driving after using marijuana is relatively common, especially among young adults and in states where marijuana is legal. Some statistics on driving high include:
- Nationwide, an estimated 14.8 million people drove soon after using marijuana in the past month according to a 2018 survey.
- About 1 in 10 nighttime weekend drivers tested positive for THC in 2007 roadside surveys.
- In Colorado, around 15% of drivers involved in fatal crashes from 2013-2020 tested positive for marijuana.
- Surveys show 16-20% of young adult drivers report driving within an hour after marijuana use.
While many people believe driving high is not that risky, studies clearly show marijuana use impairs driving ability and increases the risk of accidents.
Tips for avoiding driving while high
The best advice is to never drive impaired. Here are some tips to avoid driving high:
- Allow enough time – Don’t drive for at least 6-8 hours after using marijuana.
- Use public transportation – Take a taxi, bus, or rideshare if you need to get somewhere.
- Sleep it off – If planning to use marijuana, sleep overnight before driving.
- Ask a sober friend – Have someone who didn’t use marijuana drive you.
- Skip combining – Consuming marijuana with alcohol increases impairment.
Being a little late is a small inconvenience compared to getting arrested or causing a tragic accident. If you feel impaired at all, do not drive.
Marijuana use negatively impacts driving ability and motor skills for hours after use. No one should operate a vehicle while impaired by marijuana since it significantly increases the risk of accidents. While alcohol impairment may be more predictable, evidence clearly shows cannabis intoxication also impairs reaction time, coordination, focus, and decision making. Driving under the influence of marijuana is dangerous, irresponsible, and can have severe legal consequences. Anyone who uses marijuana should carefully plan transportation options that don’t involve getting behind the wheel for at least 6-8 hours after use.