How long does it take to get marijuana out of your hair?

Once you use a drug, it is in your hair permanently, until you quit using drugs and grow a completely new head of hair. Growing a completely new head of hair takes one to two years.

No shampoo can remove the drugs, either. Again, traces of the drug are inside the hairs themselves. It would be like trying to cleanse your blood/urine of drugs by taking a long, hot shower with lots of soap. The drugs are inside your body (and inside your hair), so washing the outside of your body/hair will not cleanse the inside.

Hair tests are 99% accurate, can detect drugs well over a year after you've used them, and are virtually impossible to cheat. If you have to take a hair test for a job, then I'm sorry to say, there is no solution besides finding another job that will not ask for a hair test. The only other option is staying sober and unemployed for like, 2 years.