1. A system for assessing a subject's analgesic state and adequacy comprising: a plurality of electrodes for obtaining biopotential signals from said subject at intervals over a period of time; a processor for (a) computing from said biopotential signals a first measure representative of the subject's sedative state, (b) computing from said biopotential signals a second measure representative of the subject's muscle activity, and (c) calculating from said first and second measures an index representative of the subject's analgesic state and analgesic adequacy.