Heal checks to identify disease (including drug addiction), or poison:
Heal check vs the Save DC at -5 to determine the source.
Heal checks can still be made "blindly", but will receive a +2 DC circumstance penalty.
You may aid another, but not take 20.
For example - you find a commoner with some debilitating condition not caused by combat. You roll a heal check to determine what the source is.
If you roll a success of the save DC -5. You identify the condition as poison called King Sleep. The save is Fortitude DC 19. 2 Saves required.
If you roll below the Save DC -5 you have you not identified the poison, the DC would be unknown in game, but a 21 (19+2).
