Combinations of compound cold medicines should be used with caution: a case series.

Background: Compound cold medicines contain multiple ingredients and are widely used to alleviate discomfort caused by viral infections. It is generally believed that compound cold medicines rarely cause serious adverse reactions; therefore, patients do not need a prescription for them. Many individuals suffer from chronic illnesses and must take medications for prolonged periods. These patients may experience serious drug-drug interactions if they self-administer compound cold medicines. Here, we report three cases of severe adverse drug reactions induced by compound cold medicines. Case presentation: All patients had a chronic disease and had been taking medication for a long time without experiencing serious adverse reactions. However, after self-administering a compound cold medicine, serious drug-drug interactions occurred. In Case 1, a 67-year-old woman with no history of coronary artery disease or angina developed angina after concurrently taking diltiazem and compound methoxyphenamine. In Case 2, a 65-year-old man who was taking propylthiouracil for a year without any adverse reactions experienced mental status abnormalities and acute liver failure after taking "CONTAC NT." In Case 3, a 63-year-old man, who was taking levodopa, entacapone, and selegiline for a long time, without any apparent adverse reactions, developed serotonin syndrome after adding CONTAC NT. These issues were resolved after the discontinuation of medication. Conclusion: Patients should consult a pharmacist or physician before using compound cold medicines to avoid the risk of adverse reactions caused by drug-drug interactions.