“All substances are poisons, there is none which is not a poison. The right dose differentiates a poison from remedy.”

(Paracelsus, 1493-1541)

Increasing amounts of a hazardous substance, such as a chemical, can increase the likelihood that an adverse event will occur or increase the severity of the adverse event.

A dose-response assessment shows the relationship between the dose of a chemical and the anticipated incidence of an adverse health or environmental effect in an exposed population.

For example, we are all aware that aspirin has therapeutic effects, relieving headaches or muscle and joint pain. Yet, too much aspirin can lead to ringing in the ears and upset stomach and bleeding. A dose-response assessment would measure the relationship between the amount of aspirin and the incidence or severity of the ringing in the ears and upset stomach and bleeding.

The dose can be increased in a few ways:

• A single large dose of the substance (a higher dose)
• Repeated doses of the substance or prolonged duration of exposure (repeated or longer exposure)
• A cumulative dose for materials that are not rapidly removed from the body