Is it safe to drive after using Cannabis?



DUI & DWI Background

old fashion drinkingThere’s a lot of debate about cannabis and driving, and the difference between cannabis and alcohol when it comes to impaired driving.



There are many differences between alcohol and cannabis.

Alcohol is a depressant substance and cannabis is an anti-depressant, and the emotional state of the driver is known to have an impact on driving abilities.

When considering driving after taking any medication remember a DUI isn’t just alcohol.

Alcohol is known as the highest prevalent substance linked to intoxicated driving with the highest incidence of deadly accidents.

A DUI and/or DWI can occur when using any kind of drug or no “drug” at all.


Any substance that can impair motor function and reasoning can be used as a cause for a DUI citation.

Allergy Medication

  • “Drugs” as defined by the State
  • Prescriptions
  • Over-the-counter medications (ie. cough syrup)

That’s right!!
  The medications you pick up at the local drug store can cause a DUI if used before driving.

In fact, most allergy medications are known for impairing the ability to drive.  And, because many of these medications contain alcohol it can show up on a test.

breathalyzer   Cannabis, on the other hand, is tricky for officials to detect,  and there are currently no breathalyzers for cannabis. (Although I have seen some articles on the development of this type of technology…cannabis breathalyzers are soon to come).

Usually when a driver is suspected of being under the influence, the first three field sobriety tests are conducted.

You can refuse to be tested, but it gives them the opportunity to demand another test (ie, breath, blood, urine) and if you refuse one of these tests the consequences are harsher.

Side Note: I’d say it’s better to cooperate when pulled over for any reason, but in this society, I have to confess it depends on things like location, skin color, cultural mannerisms, and other things that shouldn’t really be relevant.

If you are pulled over and you cooperate, expect to perform at least 3 sobriety tests. Officials are trained in giving these sobriety tests but accuracy and validity may be questionable.eye gaze

Horizontal gaze nystagmus test – In this test the eye-gaze reactions are measured
when looking over a 45 degree angle without moving the head.

Sober eyes are supposed to naturally and involuntarily jerk after the 45 degree angle, but if the eyes jerk at or before the 45 degrees it is considered a sign of impairment and can be used as evidence.

This is estimated to be 75% reliable.  (In my opinion this would be difficult to accurately determine in the field).


Walk and Turn Test – The walk and turn test splits attention between physical and mental abilities. Officials are looking for the following impairments;

  • Loss of balance
  • Counting the wrong number of steps
  • Inability to stay on the line designated for walking
  • Breaks in walking
  • Beginning before instructed

This test is considered 68% reliable.

In my opinion, dividing attention is probably not the best way to determine driving abilities.  Coming from a person who loves science and watching brain games, the brain cannot divide its attention without making mistakes in one area or the other, which makes me question the test validity.

One leg stand test – Also a test of divided attention. Officials will consider impairments during this balance test if they see;

  • Swayingwalk and turn
  • Hopping
  • Putting your foot down

This test is considered 65% accurate.

Although I might question the reliability of these tests.  There is evidence to suggest that these tests work, which is why its used as evidence in court.

Other methods of testing;

Drug swab test, a saliva test used to detect traces of drugs.  (This test isn’t 100% accurate either, because traces of the drug can stay in saliva for three days, long after intoxication has subsided.

Cannabis and DrivingCanna Drink

     Cannabis is an interesting “drug” because its effects are said to be the opposite of alcohol.  It does still cause impairment, but not in the way most believe.

Cannabis does impair psychomotor skills and reaction time, but not to the same degree as alcohol.    Risk of accidents seem to increase as blood intoxication levels increase with any type of drug.

When cannabis is isolated and subject groups are controlled for validity there is NO significant increase in accident risks.

Cannabis is the best medication when you HAVE to drive.

Cannabinoids already exist in the body, but increase in cannabinoids cause the patients to be increasingly aware of their impairment.

Cannabis patients over-compensate for their impairments.

Patients will drive slower and leave more room for reaction time in case of emergencies.

Most studies (although limited) suggest that cannabis does not increase the risk of accidents and cannabis has little effect on driving skills and abilities.

I’m not suggesting you drive under the influence, but of all the drugs that could be used with patients that need to drive, cannabis is the safest.

canna car    Since cannabis is present in the system for a very long time, it is very difficult to link cannabis to unsafe driving.

Cannabis can be present in the body at the time, without the patient being “high.”

Cannabis consumers should know that 13 micrograms of THC is equal to the impairment level of .08 alcohol.

Laws regarding cannabis impairment and consequences are different in each state. In California, possession has been decriminalized and use is legal for medical patients, but no specific laws regarding cannabis and driving.

There are many people who suffer from illnesses that absolutely need their medication.  Sometimes throughout the day, whether or not they have to drive.


It is for the sake of these people that I believe only the safest medication should be used when needing to drive. And yes, I do believe cannabis is safest medication.


Drinking and Driving;                          Cannabis and Driving;                           Photos from;                                                                                                                                        

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