Lily and Leo

 is an unmarked quest in Fallout: New Vegas.

Quick walkthrough
This quest is activated by recruiting Lily. A the first time her health reaches one-quarter in combat outside of Jacobstown, she will suffer a psychotic break and goes on a rampage. Asking her what happens reveals 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, the 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.

Depending on what option the player chooses it will effect the ending for Lily in the game.