bioactivity

Bioactivity is whether, and how strongly, a molecule actually does something to a living system. It is the practical proof that a compound is more than an inert chemical, that it can nudge a biological process in some measurable way.

Stated precisely, it is the measurable effect a compound exerts on a biological system or target. It is quantified in experiments using numbers like the concentration needed to inhibit a target by half, so that different molecules can be ranked and compared.

Bioactivity is the central currency of early drug discovery, because a molecule with no measurable effect is a dead end. However, activity in a test tube does not guarantee benefit in a patient, since a compound must also reach its target in the body and avoid harming healthy tissue.