Hello I have had testing done for a while I tested positive from hair from my head although I did not use. I then tested from my body hair and came back negative. The head hair was 90 to 100 days back and the body test was back almost twelve months. I wish to find out which is the more definitive test. I wish to also find some research papers on this subject.

J_9

I believe the hair from the head is more accurate as it grows for a longer period of time whereas the hair from the body falls out and regrows at a more rapid pace.

Research papers I am not sure of. But it just makes common sense that the hair on the head would be the more definitive answer.