Legal cannabis in Canada now has a birth date. As governments, law enforcement, and fleets gear up for Oct. 17, we’re looking at what happens when you consume a cannabis product.

Pop culture would have you believe you’ll get a little lazy, a little giggly, and you’ll be reaching for your favorite snack. But what happens really? And, more importantly, how does it affect your ability to drive?

Marijuana contains more than 420 chemical compounds, including 60 with psychoactive properties – in other words, the ones that will get you high.

Just like alcohol, how impaired someone becomes depends on a number of factors including the concentration and mix of the compounds in the strain of cannabis ingested, but also the height and weight of the person doing the ingesting. And If you’re drinking alcohol at the same time, you’re going to be more impaired than with cannabis alone.

But also like alcohol, even if you think cannabis doesn’t affect you – it could have dangerous consequences if you get behind the wheel after using it.

In a study done for Alcohol Countermeasure Systems (ACS) by Matt Goledzinowski, PhD, found that unlike alcohol, those using marijuana feel the effects almost immediately after consuming the drug, and they can last for four or more hours.

Roadside tests will be looking for drivers with 2.5 nanograms or more in their system through a combination of oral fluid tests and sight tests called Standardized Field Sobriety Tests (SFST). In provinces like Ontario, commercial vehicle drivers will be required to drive with no THC – the name of the psychoactive compounds in cannabis – in their system.

Those tests can lead to road-side license suspensions, blood tests, and eventually charges, but Goledzinowski’s report says testing isn’t always as clear-cut as it’s become with alcohol.

While alcohol is processed through the liver, THC is retained in body fat, so it can take longer to clear the system, and you can be impaired even if you no longer feel the effects.

Similar to alcohol, the ability to tolerate cannabis also depends on how often you use it. Chronic users will feel the effects less, while those who consume irregularly will see greater effects in a shorter time-frame. To get the desired effects, it’s also likely chronic users will have more cannabis in their system.

That means even if you think you’re okay to drive after just one puff, or three hours after consuming, you’re probably wrong.

Studies show that those who have consumed cannabis are more relaxed, have difficulty with concentration, can be fatigued, and can be easily disoriented. They can also have altered perceptions of time and space.

These effects make for slower reaction times, and difficulty tracking the road and maintaining control of the vehicle.

The studies Goledzinowski looked at showed the odds of a collision increased dramatically after just two nanograms in a person’s system and were seven times more likely with seven nanograms in a person’s system.

All this information assumes the user is consuming cannabis by breathing it in in some manner. The report says the most potent way to consume cannabis is to vaporize it, followed by smoking.

Even though the effects on the system take longer to appear, if a user consumes the drug by putting it into food – edibles – the concentration in the system can be much higher and last much longer, with some effects lasting as much as 25 hours.

In addition to prolonged presence in the system, consuming the drug by eating it can be dangerous to those who don’t do it regularly – not feeling the effects right away means users are prone to taking too much. When the drug begins to be absorbed in the system, there is a significantly higher risk of an overdose that way.

Canada won’t be allowing edibles right away MPP Bill Blair said back in May. Legislators will take more time to evaluate how edibles should be dosed, packaged and sold so consumers remain safe and they stay out of the hands of children.

Blair said although the law allows for under 2.5 nanograms in the system, the hope is that drivers will be completely sober when they’re on the road.

For more on the upcoming changes check out all out coverage in the July issue of Today’s Trucking or here.

This story was updated from an earlier version to correct an error. A previous version of this story incorrectly reported the legal limit was 25 nanograms. It is 2.5 nanograms. We regret the error.