Be sure to cover all hair, especially on the back of your neck. 4 Cover with a shower cap; continue to massage scalp periodically. 5 Let stand in hair for 30 minutes. 6 Repeat the above with remainder of the bottle. 7 DO NOT RINSE shampoo out until after the hair sample has been removed. 8 Get Clean Shampoo is effective for 4-5 hours before the bloodstream puts nicotine metabolites back into the h