"I use the P&S Liquid as needed - usually once a week and keep it in my scalp overnight. Same timeframe for the TARSUM medicated shampoo. The shampoo needs to be on the scalp for atleast one hour and then wash your hair as usual. I usually leave it on longer. Just be careful not to use the shampoo on the same day if you have your hair bleached. It could irritate your scalp. Good Luck."