This method is not fool proof, but does have a very high(90%+) success rate.
THC metabolites are stored in the cortex of the hair strand. The cortex is protected by a layer of scales called the cuticle. To strip the metabolites from the cortex, the cuticle needs to be opened and penetrated.
Basics open the cuticle due to their PH levels above 7. Baking soda, bleach, and ammonia are all are strong basics that help to open the cuticle.
Shampoos like Toxin Wash and Zydot contain strong stripping agents, that combined with bleaching and redying yield a very high success rate in passing hair tests.
I think going to a pro is best for bleaching and redying, but it can be done at home.
The basic plan is to bleach and redye twice. Use a 40 volume peroxide bleach. Ignore the hair pros and sign a waiver if needed. I think washing out the bleach and the dye with a very strong shampoo like Toxin Wash works best. The second bleach and redye should be done at least 10 days after the last session of herb. If you have little or no clean time, the last bleach and redye should be done as close to the test as possible.
The day of the test make a thick baking soda paste and massage it into your hair. Then do a full TW treatment and then a full Zydot treatment. These two shampoos compliment each other.
Good luck, almost everyone who does this passes...
I have no experience with them, but some people have had success with hair relaxers and perm treatments. These products contain propylene glycol and ammonia, which are proven to open the cuticle and reduce metabolites. I'd wash with TW or another good shampoo after treatment.
There is a common misconception that AloeRid Shampoo helps to pass a test. It does nothing. It is the discontinued AloeRid Treatment that contained a high propylene glycol content, and was effective.
There is a treatment program called the Macujo Method. It works for some people, especially those with thin light hair, or low levels of usage. It does not work well for heavy users with little clean time. It did not work at all for me.
Best of luck to all--Jerry G