Quote Originally Posted by Bond
I Heard they can detect from up to 3 years of smoking. Not sure if depending on how much you've smoked affects it but id think so considering... More THC means more likely to be positive.
They could test the entire length of hair but it becomes inaccurate after 1 and 1/2 inches off the scalp. In the U.S. they can only use the first 1 & 1/2 inches off the scalp, or 90 days of history.