Lily and Leo

 is an unmarked quest in Fallout: New Vegas.

Quick walkthrough
This quest is activated by recruiting Lily in Jacobstown. The first time her health drops below 25% in combat outside of Jacobstown, she will suffer a psychotic break and go on a rampage. Asking her what happened will reveal that she takes her medicine in half-doses.

A new option should now appear in her tactics interface, where the Courier can make a recommendation on what dosage of medicine she takes. If she takes her medicine in full doses, she no longer suffers psychotic breaks but becomes far less effective in combat, at half-doses she remains the same as normal, and if she does not take her medicine at all she will become much more effective in combat, but suffer psychotic breaks at half-health instead of a quarter.

Each option the player chooses will cause a different ending for Lily in the game.