[Seattle3503]

The test for marijuana aren't as useful as the tests for alcohol. Marijuana test may still come up positive long after you are impaired.

[cannaceo]

Yes, THC is lipophilic. Heavy users can take as long as 30 days to test negative.

[Zircom]

Even longer, personally failed a drug test after not smoking for 4 months. I believe it's something to do with modern test involve looking for what THC breaks down into as the body processes it instead of THC itself.