[Side effects of opioid and gene variants].

There are individual differences in the analgesic effect and the side effect of the opioid to which genetic variation may be related. Analysis of micro-opioid receptor knockout mice indicated that inhibition of gastrointestinal transit by morphine is mediated by micro-opioid receptor. Our study suggested that gastrointestinal symptom (especially loss of appetite) as a side effect of opioid could be associated with the gene polymorphism of dopamine D2 receptor. Understanding of the relationships between gene polymorphisms and opioid sensitivities may lead to more-accurate prediction of the opioid sensitivity and opioid requirements in individual patients.