Cannabis 102 – Tetrahydrocannabinol (THC)

Oct 26, 2017

Tetrahydrocannabinol – What the heck is that?

When cannabis is used the tetrahydrocannabinolic acid (THCA) in the plant is broken down, or converted, into tetrahydrocannabinol or THC which is psychoactive. Almost right away the body starts metabolizing, or breaking down, the THC to it’s primary metabolite 11-hydroxy-THC (11-OH-THC) “hydroxy THC” which is also psychoactive. The hydroxy metabolite will remain in a person’s system for approximately 24 hours but will normally fall to below 1 ng/mL after 12 hours.

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11-hydroxy-THC (11-OH-THC)


11-nor-9-carboxy-delta-9-THC (11-COOH-THC)


The body will continue to further metabolize the drug into a secondary metabolite 11-nor-9-carboxy-delta-9-THC (11-COOH-THC) “carboxy THC”. It is this non-psychoactive metabolite that remains detectable for weeks and is normally specifically screened for when urine testing.

*Note the delta-9 portion of the molecule’s description, this is where the term “screening for delta-9” came from.

Interestingly, the carboxy metabolite constitutes approximately 30% of the gross THC metabolites that are created when cannabis is used. This is why drug tests screen the gross THC metabolites in urine at 50 ng/mL and confirm at 15 ng/mL as 15 is 30% of 50.



Half-life is the scientific term to describe how long it will take for an amount of a substance to be reduced by half. So in the case of cannabis where we are looking at three different molecules, each one has a different half-life. About 4-24 hours for THC, 24-48 hours for hydroxy THC and 48-72 hours for carboxy THC. Of course, these are simply “averages” as the time is greatly affected by a number of physiological factors.

Keep in mind that these times are not the periods of detection, but just that of the molecule’s half-life which does indeed affect the detection and impairment window.


Detection Periods

There is a tonne of misinformation in the world wide web that can appear confusing and often contradicting. The reason for this is that detection periods are approximations with no hard stop.

Taking into consideration specimen types (urine, oral fluid, blood), metabolisms, quantity used and testing methadologies – it is almost impossible to construct guidelines.

Here’s our best summary:


Specimen Type

Urine detection is the longest, followed by blood and then oral fluid.

Specimen Type Days
Urine 1-30 days
Blood 1-7 days
Oral Fluid < 1 day


Fat Soluble – What does that mean?

THC molecules are fat soluble and, as a result of that, when THC is introduced into the bloodstream it accumulates in adipose (fat) tissue which slows the metabolization of the molecule.

For those that have used cannabis for a long period of time, and have gained fatty weight during this period, it is possible that rapid weight loss could release a small amount of THC back into the bloodstream and be detected in trace amounts in urine. However, the amount released would be very low and unlikely to cause a positive screening result above 50 ng/mL.

Stay tuned for the next post on THC impairment