A paial agonist can antagonize the effects of a full agonist because it has

High affinity but low intrinsic activity. The activity is mainly governed by affinity , intrinsic activity of a drug. iagonist has high affinity and intrinsic activity,antagonist has affinity but no intrinsic activity zero. Paial agonist has high affinity and low intrinsic activity. KDT 6/e pg 37