Opioid analgesics are the leading cause of adverse drug reactions in the obstetric population in South Korea

Medication use during pregnancy is gradually increasing; however, the safety of this practice remains largely unknown. We investigated medications with the most adverse drug reactions (ADRs) among pregnant women and the clinical features of those medications. Reports of ADRs among pregnant women were extracted from the Korea Adverse Events Reporting System (January 2012–December 2015). We analyzed the data of drugs frequently reported to cause ADRs and their clinical features among 3 age groups. A total of 5642 ADRs among 3428 patients were analyzed. The number of ADR reports increased annually. The most common drug categories causing ADRs were analgesics, followed by gynecologic, uterotocolytic, anti-infective, antidiabetic, analgesic, and antihypertensive drugs. Analgesics comprised 6 opioids (morphine, fentanyl, hydromorphone, oxycodone, tramadol, pethidine) and an anti-pyretics (nefopam and ketorolac). As an individual drug, ritodrine (24.4%) was the most frequently reported, followed by morphine, 5-HT(3) serotonin antagonist, nefopam, fentanyl, magnesium sulfate, insulin lispro, cefazedone, sodium chloride, hydromorphone, oxycodone, cefotetan, nifedipine, human insulin, tramadol, ketorolac, pethidine, methylergometrine, metoclopramide, and misoprostol (in that order). ADRs most frequently occurred in women aged 25 to 34 years, and the trend of ADR with the 20 most commonly reported medications significantly differed among the age groups (P = .011). In addition, the kind of common causative drugs was different among the age groups. Knowledge of medications and clinical conditions resulting in the highest ADR rates among pregnant women is necessary for medical practitioners to administer proper care.