How long does traces of drugs stay in your hair root?

In some extreme cases, traces of drugs have stayed in hair follicles for upwards of 6 months. In extraordinarily rare cases, traces have still been present after 9 months of consecutive abstinence from drug use. The traces stay in your hair root indefinetly. Ex: Aquired leg hair at age 13. Smoked Marijuana at age 15. Ten years later it will still be there.