Despite the potential therapeutic benefits, using marijuana is
currently prohibited under federal law. Additionally, testing in the workplace is common, with many people feeling their jobs may be at risk in case of detection.
As a result, many prospective and current medical marijuana users want to know how long marijuana
stays in their system so they can reap the benefits while avoiding the
potential legal repercussions.
Detecting the Presence of Marijuana
When marijuana is inhaled or ingested, tetrahydrocannabinol (THC) and
other cannabinoids are absorbed into the bloodstream. THC is detectable
in the blood for only a short time before being broken down into
molecules known as metabolites. These metabolites are stored in fat and
are eliminated from the body over time. Determining exactly how long
marijuana stays in the body depends greatly on how long THC and its
metabolites remain in the following biological specimens:
Urine
Urine reveals the presence of THC-COOH, a THC metabolite, for up to
eight days after a single use of marijuana. The accuracy of urine
testing declines after about a week, but many frequent or heavy
marijuana users continue to test positive for up to 15 and 90 days,
respectively. Diluting urine with water or other substances can increase
the chances of a false-negative result.
Hair
Hair provides the longest record of past marijuana use, and detection
times are based on hair length. It takes about 5-10 days for hair
containing THC-COOH to grow above the scalp where it can be extracted,
and moving from root to tip, every half inch of hair provides a 30-day
detection window. A standard hair test uses a 1.5-inch sample of hair
cut at the scalp line, and covers a 90-day detection period. The results
of hair analysis are not affected by external contaminants, such as hair
dyes and styling products.
Blood
THC is detectable in the blood for appropriately six to 24 hours after a
single use of marijuana. Heavy or frequent use can produce positive
results for up to a week.
Saliva
Saliva testing offers the shortest detection window and thus provides a
record of more recent marijuana use. THC is most readily detectable in
saliva one to two hours after ingestion, but can continue to produce
positive results for up to 12 hours. The results of saliva analysis are
not always reliable because only minimal amounts of marijuana are
excreted in saliva.
Factors Affecting the Elimination of Marijuana
Estimating how long marijuana stays in the body is a challenging task
because of the many factors that influence the drug’s elimination. Some
of these include:
- Amount and frequency of use: Frequent or heavy marijuana use
typically results in longer elimination times. - Metabolic rate: People with high metabolic rates break down THC
faster than those with low metabolic rates and thus eliminate
marijuana faster. - Age and overall health: Metabolism slows with age and ill
health, resulting in longer elimination periods.
The amount of time marijuana stays in the body depends on a combination
of factors that are unique to each individual. In a small percentage of
cases, marijuana may stay in the body for longer than the times
described here.
