The NFL and the NFL Players Association have tweaked the substance abuse policy. Among the changes, the threshold for a positive test has been significantly increased. PFT has obtained the new policies negotiated by the league and the NFLPA. The prior limit for THC concentration was 150 ng/ml. As of Friday, it’s 350 ng/ml. Generally speaking, it takes a week after regular use to get below 350 ng/ml. Fines will also be reduced for positive…