THC testing

THC testing detects evidence of dagga or cannabis use.  Cannabis, also known as marijuana, is a plant that produces compounds called cannabinoids, such as tetrahydrocannabinol (THC).  Cannabinoids have varying effects on the body.

THC testing is most often performed using a urine sample, but blood, saliva, or hair can also be used as samples.  Testing for THC use may be considered for a variety of purposes.  Although cannabis use can be tested alone, this test is often combined with other substances as part of a broader screening panel, such as a 5-panel drug test.

THC can be detected for a period of days, weeks, or months after use.  The length of this detection window depends on numerous factors.  For example:

• Test sensitivity. More sensitive tests can detect lower doses of cannabis.
• The amount and frequency of cannabis used. Cannabis drug tests look for THC, not cannabis.  So, the amount of THC that a person consumes is a significant factor.  The effects of THC are cumulative.  This means that a person who smokes several times over several days has consumed a higher THC dose than someone who smokes once, so they are more likely to test positive.  The strength of each dose of THC also matters.
• Body fat. THC is a fat-soluble compound.  This means that fat cells store cannabis.  As such, people with higher body fat concentrations may metabolize cannabis more slowly than a person with less body fat.
• Sex. Typically, females have more body fat than males.  This means that females may metabolize cannabis slightly more slowly.
• Hydration. Dehydration increases concentrations of THC in the body.  While drinking lots of water is unlikely to affect a THC drug test significantly, severe dehydration might.
• Metabolism. For a drug test to be negative, the body must eliminate THC from the system, as well as metabolic chemicals that have links to THC.  People with faster metabolisms typically eliminate THC more quickly than those with slower metabolisms.
• The type of sample used. This is because of the way the body metabolizes THC.  THC is a lipid-soluble chemical.  This means that it binds to fat in the body, that increases the length of time it takes for someone to eliminate THC.  Cannabis use detection windows:
  • Blood For a few hours
  • Hair Up to 90 days
  • Saliva Up to 24 hours
  • Urine Casual user 1-3 days, moderate user up to 10 days, 6-12 weeks in habitual users

What does the test measure?

Drug testing for dagga or cannabis measures cannabinoids or cannabinoid metabolites in a sample of blood, hair, saliva, or urine.  Metabolites are substances created when the body is breaking down a drug.  Cannabis produces over 100 different cannabinoids, but only a few cannabinoids and their metabolites are measured in cannabis testing.  Dagga tests usually measure delta-9-THC, the primary psychoactive cannabinoid in cannabis, and/or its metabolites.

Interpreting test results

Testing negative on a cannabis test indicates that the cannabinoids or metabolites measured were not found in the test sample.  This may be because the person has not used cannabis, the cannabis use was outside of the detection window, or that the level of this drug was below the cutoff level for a positive test result.

A positive cannabis test indicates that cannabinoids or metabolites were detected in the test sample.  A positive drug test result requires additional confirmation testing conducted in a laboratory.

Cannabis testing and “second hand” smoke

You may be concerned about the possibility of a positive THC test result due to passive or second-hand exposure to cannabis smoke.  Research suggests that testing positive after second-hand exposure to cannabis smoke is unlikely as metabolite levels in the body aren’t sufficient to be detected in urine drug tests (the urine concentrations of THC will not be above the cut-off sensitivity level of the test).