Combined pharmacotherapy of pain in a patient with cancer disease raises risk of potential drug interactions. They include interactions pharmacodynamic in character, for example with agents exerting depressant effect on CNS, as well as pharmacokinetic- with multiple substrates, inhibitors or inducers of CYP 450. The paper presents an overview of literature concerning drug-drug interactions of strong opioids employed in cancer pain treatment. It is the continuation of the article on the interactions of opioids of the second step of WHO analgesic ladder, published in previous volume. Key words: strong opioids, drug interactions, serotonine syndrome, respiratory depression.