Because paracetamol is what Americans generically call acetaminophen --though it's more commonly known in AmE by the brand name Tylenol. Both names, paracetamol and acetaminophen, are based on the description of the chemical components in the drug--they both make mention of the acet part.
Is paracetamol illegal in the US?
Paracetamol is not banned in the U.S. It is called acetaminophen and is sold over the counter. From Wikipedia: Acetaminophen is the name generally used in the United States, Japan, Canada, Venezuela, Colombia, and Iran; paracetamol is used in international venues.
Can you buy paracetamol over the counter?
Over-the-counter painkillers are painkillers that you can buy from a pharmacy or shop, without needing a prescription from your GP. These include paracetamol, ibuprofen, low-dose codeine and aspirin.