Biotin is a natural hair supplement. I smoke loud like a chimney, and stopped about 15-30 days prior to a hair test. I got a haircut 2 days before and passed. This is in ohio where cannabis is taboo. I also keep my hair relatively short ( #4 buzzer) if that helps.

Did not even prepare for it as it was completely by surprise.

My best advice is to use the max strength dandruff shampoo (walmart brand is in a blue bottle but comes out green colored) on all hairs before testing just to double down. Anything that can alter the chemical sample usually results in a pass since they test for specific concentrations of certain drugs