Marijuana or THC has been used for thousands of years, starting in ancient China, for medical and recreational reasons. For years, people have speculated about the true meaning of 4-20. Some popular myths about the origins of 4-20 include that the number is the police code for marijuana, it’s the number of chemical compounds found in weed, or it has some connection to Adolf Hitler’s birthday, April 20, 1889. States like Colorado, where it’s now legal to smoke marijuana are bracing for an influx of tourists around April 20.
Some people worry about how long THC will stay in the system after using it and the trouble they could get in if caught with a drug test. Many employers test for cannabis use, such as several call centers, Costco, Safeway, and Subway.  After smoking, the effects of using marijuana will usually go away quickly, but can still be detected in the body for weeks or longer at a time. This depends on how much and how often it is used. Since marijuana does not stay in the bloodstream for a long time, blood tests are not often used to detect it in the body. In marijuana there are some metabolites (a substance formed and used for metabolism) that last around 20 hours in the body. Sometimes these metabolites can be stored in body fat and can remain there for around 10-13 days. This could all depend on how often the user smokes though, regular smokers have been reported positive after 45 days since the last use and 90 days (almost three months) for heavy users.

Urine tests for marijuana have become more accurate and although there are sometimes false positives, it is now very hard for that to happen. It is very hard to fool a test used to determine whether or not you have marijuana in your system. There are many urban legends online telling people of the ways to fool the test, but most are not true.  Things such as drinking a lot of water will not remove all THC metabolites, using herbs may not work, most have to be used over a long period of time but by the time that is over the body could have removed it itself, and tampering with the test, adding things such as bleach, salt, and detergent usually won’t work.

Overall the only true way to not get caught is to stop using it, but if that’s not the case then perhaps it is time to quit the job or accept whatever happens next.

Source: Verywell.com