I was wondering how far a hair follicle drug test goes back. why i was asking was because of a job, someone said they go back 6 months for this job?

About right: Depends on the length of the hair, but the average size hair will go back about 6 months. There is variability in hair growth, and depending on whether someone is fair-skinned or dark, the hair may retain certain drugs differently. But in general, its about 6 months worth. The larger question is whether an employer has any right to determine what someone does during off-time not working.