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 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 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.
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 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:
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.