On the other hand, if an employer wants to examine his staff’s drug usage over a long period, perhaps for a quarterly review, he or she should choose the hair follicle test. Traces of drug use, even up to 2 months after the illicit substance was last used, can be detected by hair follicle testing. This is also a less intrusive option for large workforces, as it simply requires a few strands of hair to be plucked, rather than dealing with bodily fluids. Knowing which drug testing option you may need for certain circumstances is essential for any conscientious employer.