How long does pot stay in your system? Good to know if you got a job interview coming up or a visit from the P.O. Officer or you’re hitting a weed DUI checkpoint.

There is a legal limit set for blood cannabinoid concentration in seven countries in Europe and many states in the US. Just like alcohol, if your concentration level exceeds legal limits, then you can be convicted. However, what happens if it has been a few days or months since you last smoked?

The metabolites, which are small molecules that are produced by the metabolism of marijuana’s chemical compounds, are what drug screens detect. When you consume pot, your liver metabolizes THC by taking HydroxyTHC and converting it into THC Carboxylic Acid. THC Carboxylic Acid is a fat-soluble metabolite that slowly leaves the body.

When you smoke pot, it takes only minutes for it to enter your bloodstream and most times, it will leave within 24 hours. It can still be detected in your urine, but urine screens are not accurate on how long it has been since you have consumed. Once your body converts the THC-to-THC Carboxylic Acid, it can be detected in your urine for roughly 13 days.

So, how do some urine tests show THC Carboxylic Acid after three months? In a study performed on a Norwegian woman back in 2009, it was shown that chronic smoking of pot causes the length of detection time to be extended. When 25 people were analyzed who were frequent users after they were forced to go without marijuana for a week. The tests showed that the whole blood THC levels were varied between participants, including nine of them not having any trace. However, six participants still showed to have high THC levels in their blood after the seven-day period.

What this study shows is that it is hard to determine how long it has been since you have last smoked, especially if you are a frequent user. It also shows that the states in the US that have a zero tolerance for pot metabolites is more likely to catch frequent users, not someone who has just had a joint the day before.