To be more precise: It is not so much a (dose) threshold but how much margin/reserves your body still has. For example kidney injury is progressive, and by the

To be more precise: It is not so much a (dose) threshold but how much margin/reserves your body still has. For example kidney injury is progressive, and by the time the kidney's functional reserve is exhausted, things will remain bad until death or kidney transplant. Also for diseases like HIV/AIDS, the cognitive reserve influences how long it takes until HIV associated dementia sets in.