Drugs.com describes Tylenol 4 as an opioid pain medication. Also called Tylenol with codeine #4, Tylenol 4 combines acetaminophen, a non-narcotic pain reliever, and codeine, a narcotic pain reliever, to relieve moderate to severe pain. While the acetaminophen has little potency as a pain reliever, it increases the effects of the codeine.
WebMD explains that codeine works in the brain to change how the body feels and responds to pain, while the acetaminophen reduces a fever. Drugs.com warns against using Tylenol 4 with alcohol, sedatives, tranquilizers and other narcotic medications. The site also warns that a dangerous drug interaction may occur with MAO inhibitors, such as isocarboxazid, linezolid, phenelzine, rasagiline, selegiline and tranylcypromine, if a person takes Tylenol 4 within 14 days of taking one of these substances.
WebMD also mentions a few of the side effects that may occur, including nausea, vomiting, constipation, lightheadedness, dizziness and drowsiness. Tylenol 4 may also have rare but serious side effects, such as fainting and seizures. WebMD also explains that severe allergic reactions rarely occur but produce symptoms like rash severe dizziness, trouble breathing or itching and swelling in the tongue, throat or face when they do occur. Drugs.com also recommends that individuals stop taking the drug if skin redness appears or a rash that spreads and causes blistering and peeling occurs.