Advantages of Hair Testing:

•  Hair testing is the most effective way to confirm long term patterns of use.
• Hair testing requires only a small sample of hair that is collected under direct supervision without any invasion of privacy.
• Suspicious parents may be able to collect a sample from a comb or a brush for hair testing without the teenager's knowledge. This method of collection is most useful for parents who want to avoid asking their children to take a urine drug test.
• Hair testing samples are hard to switch compared to urine samples prior to a drug test, where many often get a "clean sample" of urine from a friend. 
• Hair testing is a good method for pre-employment testing where the goal is to eliminate applicants who regularly use drugs.

Disadvantages of Hair Testing:

• It takes approximately 7-10 days for drugs to show up in hair.
• For post-accident or reasonable suspicion testing, a hair test cannot be done immediately after suspected use.
• For parents who want to test for recent use, hair testing may not be the best method.  Instead a urine or oral fluids test can detect recent use. 
• Hair testing tends to be more expensive.