When you should give chems to Mama Murphy and when you should not give chems to Mama Murphy.
A side quest in Fallout 4 is called Power of the Sight. You can use this whenever you get it to tight spots in the game, but be very careful. If you give too many chems to Mama Murphy, you will kill her.
Freedom Calls is a freebie. All you have to do is talk to her over speech check to find the Deathclaw.
Do not give her chems during the following quest: Do not give her chems during Jewel of the Commonwealth, Do not give her chems during the second phase of Getting A Clue and On the Trail, Do not give her chems during Reunions, Do not give her chems during the quest Glowing Sea, and do not give her any chems when you join a faction.
When to give her chems: Give her chems before you start the quest Unlucky Valentine she will give you the password to get past Skinny Malone and Darla, Give her chems before the first phase of Getting A Clue and On the Trail this will tell you where Kellogg's keys are or you are going to have to pick the lock which is an expert lock, and finally give her chems when you do Hunter Hunted this will give you the password to deactivate the coarser or you are going to have to kill him if you do not get that password.