Imagine this. You’re over at a friend’s house and the two of you smoked a joint. It’s been a couple hours, you don’t feel the effects anymore, and now you’re planning on driving home. But has the cannabis completely left your system?

It’s hard to know!

Our bodies process alcohol and other substances much differently than cannabis. We can usually tell when alcohol has left our systems. But what about cannabis? How long does it take for cannabis to completely leave your system? If you work in a safety sensitive job or you sometimes drive after using cannabis, it’s important to know the basic facts!


What are the Rules?

Similar to driving with alcohol in your system, there are some pretty strict rules about driving while impaired by cannabis. The Government of Canada says there are two prohibited levels for THC. The less serious offense is to have between 2 nanograms (ng) and 5ng of THC per ml of blood, while the more serious offense is to have 5ng or more of THC per ml of blood. Both of these are punishable with a $1000 fine and even jail time.


How Much Cannabis Can You Consume?

There’s not enough research to know how much cannabis you need to consume to be considered impaired. However, forensic toxicologist Jim Wigmore says that you’ll get about 120 nanograms of THC in your blood from an average joint. He also goes on the say that after about two and a half hours, that blood concentration will drop to about half – so 60ng. After this, the cannabis metabolizes at a slower rate.


How is Cannabis Metabolized?

The way that cannabis is metabolized in the body directly affects how long you’re able to detect its presence. Cannabis – THC specifically – is fat-soluble. This means that while your liver still helps to metabolize the THC, it will also bind to the fat in your body, causing it to linger for longer periods of time than, say, alcohol.

In an interview with Global News, Dr. Mann explains that “when you use cannabis, the THC gets absorbed into the fat in your body, and so there’s kind of a reservoir there that keeps getting released fairly slowly, so that you will find trace amounts of THC in the blood for longer periods of time, but at very low levels.”


How Long Can You Detect Cannabis?

Unfortunately, there’s no easy answer for this. After smoking it will take you a few hours to come down from your high. Still, this doesn’t mean that the THC has actually left your system.

While alcohol will disappear from your body within a few hours, this doesn’t happen with cannabis. Different drug tests can detect THC in your body for months after use. The amount of time cannabis stays in your body depends on a couple different factors, including:

  • Body fat
  • Frequency of use
  • How you consume it
  • How much you ingest
  • The sensitivity of the drug test.

Of course, this is all unique to individuals and relies on how quickly your body metabolizes the drug. So, for now, it’s impossible to say how long cannabis will last in your body, but there are more and more studies being done on this every day.


Should I Drive?

The rule here is the same as when it comes to alcohol – if you’re not sure, play it safe to avoid fines, convictions, and even arrest. Call a taxi or an Uber, stay over at your friend’s house, or wait it out a bit longer.