Serotonin syndrome after an overdose of over‐the‐counter medicine containing dextromethorphan

Serotonin syndrome is a potentially life‐threatening adverse reaction from therapeutic drug use, intentional self‐poisoning, or inadvertent interactions between drugs. We report a case of the serotonin syndrome after an overdose of a commonly available over‐the‐counter cough medicine, Shin CONTAC sekidome daburu jizokusei. Over‐the‐counter drugs containing dextromethorphan may, in rare cases, cause health problems requiring hospitalization or worse. An appropriate explanation from the pharmacist at the time of purchase, although not mandatory, is recommended.