Dear Alice,

How long does marijuana stay in the body?

Dear Reader,

Puff the magic dragon, Mary Jane, hash, pot, whatever you want to call it, marijuana itself doesn't actually stay in the body. However, some of the chemicals in the drug do, such as THC (delta-9-tetrahydrocannabinol), the substance in pot that's mainly responsible for people's high. Although THC loses its effect on the brain after a few hours, detectable traces may remain in the body for a while longer. THC bonds to fat cells and the stored THC slowly breaks down during metabolism and clears itself from the body. The amount of time this takes varies drastically from person to person and depends on:

  • How much pot is used
  • The method and frequency of use
  • The user's rate of metabolism
  • The concentration of THC in the marijuana plant

In testing to see if someone has recently used pot, there are two important substances to keep in mind: THC and 9-carboxy-THC. 9-carboxy-THC is a product of the body's metabolism of THC and, more importantly, it's detectable for a longer period of time than THC is detectable. This is the reason that drug tests, namely urine tests, look for 9-carboxy-THC.

Many of the following numbers are estimates.

Typical Periods of Time that Marijuana Use May be Detected


Blood Tests

Urine Tests






Frequent Users*

4 to 8 hours

2 or more weeks

10 to 21 days


Infrequent Users**

3 to 4 hours

2 to 3 days

3 to 7 days


Some private companies may use hair tests to detect possible marijuana use. Positive hair test results have been found to be unreliable.
* Frequent users are defined as people who use marijuana several times per week, or more often.
** Infrequent users are those who use marijuana seldom enough that THC and/or 9-carboxy-THC are no longer detectable before their next use. In essence, these users do not use pot often enough to allow for the tested substances to build-up from one use to another.
†The detection period for 9-carboxy-THC in urine may be as long as three months in extremely heavy users. 

Research on saliva tests indicated that they may be able to detect THC up to eight hours after ingestion but they aren't widely used. Additionally, exposure to second-hand marijuana smoke may result in a positive urine test within one to two days although it's unlikely.

Though the motivation for your question is unclear, it's worthwhile mentioning that some employers drug test their employees. If you're concerned about this, you may want to weigh the pros and cons of using marijuana or other substances against the consequences of testing positive.


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