Opium, Street Opium, and Cancer Risk

Opium is defined as the air-dried latex obtained by incision from the unripe capsules of Papaver somniferum L. Opium is a complex mixture that contains approximately 10% morphine and 2% codeine. It is commonly used to prepare opium tinctures for people with chronic diarrhea. Morphine and related opioids are powerful but highly addictive analgesics; designing less addictive opioids is an active area of pharmaceutical research that may lead to significant improvements in chronic pain management. Recently, the International Agency for Research on Cancer (IARC) has classified opium consumption as carcinogenic to humans (Group 1) based on sufficient evidence of carcinogenicity in human studies. However, all human studies analyzed by the IARC Working Group included participants who consumed opium that was mixed, adulterated, and/or contaminated with known and probable human carcinogens (e.g., tarry residues of combusted opium, arsenic, lead, and chromium). The working group considered that these carcinogens were part of the complex mixture that opium is, rather than co-exposure or confounders. No evidence of carcinogenicity was available for pure opium in human, animal, or mechanistic studies. To avoid confusion and concern among health professionals and patients using medicinal opium preparations and in scientists involved in the design and development of new opium derivatives, opium should be classified in Group 3 (not classifiable as to its carcinogenicity to humans). The term 'street opium' could be used to refer to opium that probably contains human carcinogens not present in pure opium and should remain in Group 1 (carcinogenic to humans).