Concurrent administration of monoamine oxidase inhibitors MAOIs or within 2 weeks of discontinuation of their use is contraindicated. MAIOs are known to interact with narcotic analgesics producing central nervous system excitation or depression with hypertensive or hypotensive crisis.
Morphine should be used with caution in patients who are concurrently receiving other central nervous system depressants including sedatives or hypnotics, general anaesthetics, phenothiazines, other tranquilizers, muscle relaxants, antihypertensives and alcohol. Interactive effects resulting in respiratory depression, hypotension, profound sedation or coma may result if these drugs are taken in combination with the usual doses of morphine.
Cimetidine inhibits the metabolism of morphine.