Years may have been a stretch. Looks like 7 days has been shown in a lab, and the CDC thinks weeks. http://healthland.time.com/2013/09/17/one-toke-many-hits-ex

Years may have been a stretch. Looks like 7 days has been shown in a lab, and the CDC thinks weeks. http://healthland.time.com/2013/09/17/one-toke-many-hits-exercise-could-trigger-additional-high-for-marijuana-users/ http://healthland.time.com/2013/09/17/one-toke-many-hits-exe... http://www.cdc.gov/mmwr/preview/mmwrhtml/00001143.htm http://www.cdc.gov/mmwr/preview/mmwrhtml/00001143.htm