Drug abstinence effects: opioids.

The capacity to produce physical dependence is an important factor in the abuse liability of the opioids, contributing both to their reinforcing efficacy and to the negative public health consequences of abuse. Validated methods for measuring the physical dependence capacity of opioids in humans are the Direct Addiction and Substitution/Suppression tests; however, both methods require that subjects be made physically dependent on morphine or on high doses of investigational drugs. New methods need to be developed. Possibilities include assessment of acute physical dependence and the modification of existing substitution test methods for use with subjects already dependent on therapeutic agents.