How long does marijuana stay in the system and when can it still be detected on a drug test?

Q:

How long does marijuana stay in the system and when can it still be detected on a drug test?

A:

Both the employer and the employee (or job candidate) can have concerns about the accuracy of a drug screen test. Detecting marijuana can be complicated, because of the variables involved regarding use and type of testing.

The active ingredient in marijuana, the one that produces the high feeling, is THC (tetrahydrocannabinol or delta-9-THC). THC enters the bloodstream quickly after being smoked; if it’s taken orally, THC will be detectable after 20-90 minutes. The liver breaks THC into smaller chemicals, called metabolites, which are stored in the body’s fat cells and slowly excreted by the kidneys and bowels.

Frontiers in Public Health reports that urine screening can provide positive THC metabolite results for a range of 10 days for an occasional user to 14-30 days for a regular user. Because THC metabolites are stored in fat cells, a heavy user can have a positive result for 30-60 days.

Hair follicle tests can detect marijuana use for up to 180 days, although they will not likely pick up someone who has used marijuana once or twice. However, follicle tests do not give information regarding patterns of use or amounts. Saliva testing shows use within a few minutes up to 18 hours, indicating very recent use.

Factors in Detection of Marijuana:

  • A person with a high Body Mass Index (BMI) will have more fat to absorb the THC. It will take longer to leave the system.
  • How often and how long a person has been smoking can affect the test result, because of fat storage.
  • Strength of the marijuana will influence the test result. The higher the potency, the longer it stays in the body. For example, 15% THC potency equals taking 5% three times.

False positives are rare. Samples that indicate the possible presence of THC metabolites are rescreened with another method. Passive inhalation of marijuana does not give a positive result because of the low amounts actually inhaled.

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Written by Suzanne Ball
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Suzanne Ball is an experienced Registered Nurse with a Masters Degree in Health Sciences. She has worked in a variety of settings, including acute care, quality improvement, and research. She is a freelance writer who specializes in writing about medical and health topics.

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