Before combining cold remedies or painkillers, check the ingredients: only one product should contain acetaminophen
Many cold remedies contain acetaminophen, also called paracetamol. Taking two such products together doubles up on the same drug, and an overdose can damage the liver. In a US study of acute liver failure caused by acetaminophen, nearly three in ten patients died without receiving a transplant. The cited Chinese over-the-counter labeling recommends no more than 2 grams a day. Avoid alcohol while taking it, too.
What it takes
Nothing. Spend a minute or two reading the ingredients on each package.
What you may gain
Over six years, 22 US hospitals prospectively recorded 662 cases of acute liver failure. Acetaminophen caused 275 cases, or 42%; the median amount ingested was 24 grams. Of these 275 patients, 131, or 48%, had overdosed unintentionally. Among the unintentional overdoses, 38% involved two or more acetaminophen-containing products. Overall, 27% of the 275 patients died without a liver transplant, and 8% received a transplant. In 2020, China's National Medical Products Administration required over-the-counter labeling to warn that overdose can cause serious liver injury and to recommend a maximum daily dose of 2 grams. Labels must also advise avoiding combinations with other products containing acetaminophen or other fever-reducing painkillers where possible. US regulations require the first liver warning on these over-the-counter products to identify three risks: exceeding the maximum daily dose, taking another acetaminophen-containing drug at the same time, and consuming three or more alcoholic drinks every day while using the medicine.
Context & considerations
On Chinese packages, acetaminophen may also be called 扑热息痛. Combination cold medicines whose generic names contain 氨酚, such as 氨酚伪麻 or 氨咖黄敏, contain it. If you are unsure, show every package to a pharmacist. The evidence is rated B because the US figures come from a case registry without a control group; they do not measure how many incidents ingredient checking prevents. The benefit is rated large because of the severity of the outcome: nearly three in ten of these acute liver failure patients died without transplantation. The 2-gram limit here is the cited Chinese labeling requirement, not a universal instruction for every product, age, or country.
Research & references
Larson AM, Polson J, Fontana RJ, et al.; Acute Liver Failure Study Group (2005). Acetaminophen-induced acute liver failure: results of a United States multicenter, prospective study. Hepatology, 42(6):1364–1372. https://doi.org/10.1002/hep.20948; China's National Medical Products Administration, Announcement on Revisions to the Labeling of Immediate- and Extended-Release Acetaminophen Preparations (No. 15 of 2020), Attachment 2, Requirements for Revisions to Over-the-Counter Labeling of Immediate-Release Acetaminophen Preparations, reproduced by the Hunan Medical Products Administration. http://mpa.hunan.gov.cn/mpa/xxgk/tzgg/wjtz/202003/t20200311_11809335.html; 21 CFR 201.326(a)(1)(iii)(A), Liver warning. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-C/part-201/subpart-G/section-201.326