The mixed agonist-antagonist drugs often cause sedation at analgesic doses. Dizziness, sweating, and nausea may also occur, and anxiety, hallucinations, and nightmares are possible adverse effects. Respiratory depression may be less intense than with pure agonists but is not predictably reversed by naloxone. Tolerance develops with chronic use but is less than the tolerance that develops to the full agonists, and there is minimal cross-tolerance. Physical dependence occurs, but the abuse liability of mixed agonist-antagonist drugs is less than that of the full agonists.