Weakening

When a baseline human is brought to Underhill, or a descendant of the original Gene War survivors without strong enough ties to an ancestor, there is a sort of test the planet puts them through. Those who die on eating the food, either plant or animal, are considered unworthy. Those who can eat the food and survive are considered worthy of remaining. Those who eat too much of the food, or are born on the planet and then sent to earth (Changlings) will most likely die of withdrawal and Weakening if they do not return to the Planet soon enough.

Transmission & Vectors
Certain survivors of the Gene Wars, and their descendants, are less susceptible to both the high and low effects of the Privatio compound found in nearly all plants and animals on Underhill.

Causes
Ingestion of food from Underhill introduces the compound to the person

Symptoms
When ingested, the Privatio compound heightens mental abilities, and in some cases, allows for communication with the altered denizens of the planet.