Not suitable as substitute in opioid-dependent patients. Discontinue use if serotonin syndrome is suspected. Patients at risk for resp depression eg, substantially decreased resp reserve, hypoxia, hypercapnia, preexisting rep depression; head injury, increased ICP, patients prone to convulsive disorders or shock; history of epilepsy, patients susceptible to seizures; adrenal insufficiency. CYP2D6 ultra-rapid metabolisers. Long-term use. Concomitant use w/ drugs lowering seizure threshold; alcohol, other CNS depressants; benzodiazepines; serotonergic drugs. Severe hepatic & renal impairment; dialysis. Not recommended during pregnancy. Not to be used during lactation. Not recommended in childn <12 yr. Elderly >75 yr.