Norco 10-325 mg is an opioid drug that treats moderate to severe pain. Opioids help treat pain by affecting the transmission of pain signals to the brain and changing the emotional response someone has to pain. While hydrocodone and other opioids can be effective at relieving pain, they can also be very addictive. Acetaminophen is an over-the-counter pain reliever found in brand-name Tylenol. Acetaminophen can be combined with opioids to increase their ability to relieve pain. While acetaminophen is relatively safe, doses that are too high can cause liver damage or failure. Because of this, Norco has a maximum acetaminophen dosage of 325 mg.