Concomitant use of other CNS depressants, such as other morphine derivatives (analgesics and antitussives), general anaesthetics, skeletal muscle relaxants, sedative antidepressants, sedative H1 antihistamines, barbiturates, anxiolytics (ie benzodiazepines), hypnotics, antipsychotics, clonidine and related substances may produce increased CNS depressant effects.