I recently went for a drug test (Early December) for a new job but it went for further testing (so it came up positive I assume) the ONLY drug I've taken in the last year is cannabis, no uppers,downers, codeine, paracetamol - nothing. The last time I had cannabis was about a third of a joint at the beginning of September this year. I was smoking on and off from January to mid July maybe 6/7 joints a week every three weeks. Then I stopped from July until this one-off joint in September and like I said nothing since. I am overweight (BMI) of 32. I don't exercise but I had two jobs all over summer (up until the end of october) which were both fairly physical - lots of walking around lifting carrying small weights etc. Anyway everything I have read says I should pass a drugs test because the last time I smoked cannabis was more than 90 days before the test (100 I believe) and that was a very small amount

Why have I tested positive when I have taken no drugs other than cannabis but over 90 days ago?