How long does weed stay in your system? There's one particular time frame that always gets mentioned: 30 days. Unfortunately it's not that simple. Marijuanacan linger in your body for a longer — or shorter — period of time depending on a variety of factors. This is due to the properties of tetrahydrocannabinol, the primary psychoactive ingredient in cannabis. THC is fat-soluble, not water-soluble, which means it stores longer in the body.