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What is the difference between cannabis usage and impairment?

Region: Ontario Answer # 2552

What is considered impaired driving due to drugs or alcohol?

You do not have to exceed the legal blood alcohol or THC blood limits to be charged with impaired driving. The only requirement for a charge of impaired driving is that your ability to drive was affected by alcohol or drugs, regardless of how much or how little was actually consumed.

Impairment by THC

Cannabis contains both CBD (cannabidiol) and THC. THC is the primary psychoactive component of cannabis that causes mind-altering effects and can impair motor or mental functions.

In contrast, CBD is the chemical component that does not get a user high and is often used for medicinal purposes.

What are the prohibited amounts of THC?

Under section 320.14 of the Criminal Code, there are 3 new cannabis impaired driving offences:

  1. Summary offence: 2 ng but less than 5 ng of THC per ml of blood.
  2. Hybrid offence: 5 ng or more of THC per ml of blood.
  3. Hybrid offence: for a combination of 50 mg of alcohol per 100 ml blood + 2.5 ng or more of THC per ml of blood.

To see the drug categories and limits for drugs other than cannabis, refer to the Blood Drug Concentration Regulations.

However, cannabis can affect each person to varying degrees depending upon many factors, such as:

  • how cannabis was consumed (smoked, inhaled, or ingested);
  • how much cannabis was consumed; and
  • what type of cannabis was consumed and its THC levels.

As well, how you consume cannabis affects how it appears in your system. For example, when you smoke or vape cannabis, you will feel the effects faster, but they may disappear between 30 minutes to 4 hours. When consuming edibles, the effects the effects may not be felt as quickly, but they will usually last between 4 to 6 hours, which is important to remember if you are planning on driving after consuming. For more information, refer to How long does cannabis stay in your system after consumption?

Police can conduct blood tests to determine the approximate amount of THC in your system. In additon, the Cannabis Act provides for oral drug screening devices that can be used by police to test for drug impairment.

Signs of impairment by THC

Consuming cannabis that contains THC can impair your behaviour and ability to drive in many ways. For example, it can:

  • affect motor skills and coordination;
  • delay a driver’s reaction time;
  • impair both short term memory and concentration;
  • cause drivers to vary speed and drive erratically;
  • reduce a driver’s ability to make decisions quickly or handle unexpected events, such as a pedestrian running in front of them

Someone who is impaired by cannabis may also exhibit the following physical signs:

  • rapid heart beat
  • smell of cannabis
  • dry mouth or shallow breathing
  • red or watery eyes


If convicted of driving while impaired by cannabis or other drugs, drivers face penalties under the Criminal Code that include suspensions, fines, possible jail time, and a criminal record.

In addition, convicted drivers face penalties under provincial Highway Traffic legislation, which include licence suspensions and fines.

For more information on drug-impaired driving offences and penalties, refer to What criminal laws apply to driving while using cannabis?

To erase your criminal record for simple cannabis possession or any other criminal charges, call toll-free 1-888-808-3628 or learn more at Pardon Partners. It’s easier than you think.

For legal advice and assistance with a cannabis related matter, contact our preferred cannabis law expert, Harrison Jordan Law .

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