What is the definition of pharmacologically active substance?

The term "pharmacologically active substance" is any chemical or substance that affects the physiology, the function of the body of a human or animal. These substances can be artificial or natural, i.e. those created by the body in response to stimulation or injury.

This term is frequently used to specify chemicals within a derivative (from a plant or animal source), those that actively affect a part of the body or its activities. It has also been used specifically to describe the alkaloid nicotine in proposals to restrict smoking.