Common side effects of using acetaminophen/codeine no. 3 that would require medical attention include shortness of breath and pale or blue lips, fingernails, or skin, according to Drugs.com. Other side effects may include black, tarry stools, generalized weakness, hives or sore throat. These side effects apply to oral capsules, tablets and liquid formulas.
Drowsiness, lightheadedness, nausea and vomiting are the most frequently reported side effects, as listed on Drugs.com. Drowsiness and dizziness are reported between 1 and 10 percent of the time and are signs that the medication is affecting the body’s nervous system. The medication’s effects on the gastrointestinal system may include constipation and abdominal pain.
Redness of the skin or a blistering, peeling rash are signs of a severe reaction, reports Everydayhealth.com, which advises seeking medical attention. Severe skin reactions may be fatal and may occur even if the individual has had no such reaction in the past. If this reaction does occur, it may be an adverse effect of the acetaminophen, and Everydayhealth.com warns that the individual should avoid acetaminophen products in the future. The Food and Drug Administration states that this is a rare acetaminophen risk, notes WebMD. Those with liver disease or other conditions affecting the hepatic system should be aware that taking acetaminophen could result in serious side effects.