The human body is speckled with tiny fat cells. These cells work a bit like the body’s storage system; when too much of a substance is available, the body stashes the excess in these cells for use at a later date. Then, the body pulls out of this storage for the following days, weeks and months. When a user takes in marijuana, this storage system plays a key role. The user is flooding the body with a substance, and the body tends to deal with that flooding by recruiting the fat cells. This can dramatically increase the time that the drug stays present in the body. See Related: Marijuana Addiction.

A Technical Explanation

Some drugs aren’t fat-soluble. In other words, these drugs don’t dissolve inside of fat cells. When a user takes in these drugs, the body must simply expel them again, as they can’t be stored. Marijuana, by contrast, can be broken down into a fat-soluble format. In fact, the active ingredient in marijuana (THC) is incredibly fat-soluble. When a user takes in marijuana, the body shears off THC, uses some of it and stores the rest. Then, as days pass, THC is slowly metabolized by the body.

Urine tests for marijuana rarely screen for the drug itself. In fact, the tests don’t even look for THC. The tests look for the chemicals that break down THC. If these chemicals show up in the urine, it means that marijuana is still present in the body. When determining how long marijuana stays in the body, urine tests provide a bit of a gold standard.

According to the National Highway Traffic Safety Administration, urine tests for marijuana will be positive within one to three days of use. However, some tests have detected marijuana in users up to five weeks after use. The cause of this discrepancy can sometimes be attributed to:

  • Age
  • Poor health
  • Gender
  • Amount of body fat

But often, the amount of marijuana the person has used in the past holds the most sway. The more marijuana the person uses, the more marijuana is stored in that person’s body, and the longer it will take for the system to clear. A study in the Journal of Chromatographic Science makes this link quite clear. People who took marijuana as part of this study, and who had used marijuana frequently in the past, had higher rates of THC on subsequent testing than did people who had never used marijuana before the study began. Frequent users seem to overwhelm their systems, even with low levels of the drug, and as a result, they can have positive marijuana test results for months longer than people who don’t use marijuana frequently.

Final Thoughts

Marijuana may cause side effects that the user can feel for hours after taking the drug, but in the days and weeks that follow, the drug is still in the body, and the body is working hard to remove it. It can show up on drug screening tests, costing a person employment opportunities, and it can continue to impact the way the person thinks and feels. It’s not a drug that is removed quickly.