Cotinine is the 'major metabolite' of nicotine. That is, it is produced by the body while breaking down, or metabolising, nicotine.

It is generally only found in the body as a result of nicotine intake, and is thus used as a measure of how much cigarette smoke has been absorbed (in the smoker) or how much nicotine (in the case of, for example, an unborn child).

Empirical formula: C10H12N2O