Codeine works by stopping pain signals from travelling along the nerves to the brain. The most common side effects of codeine are constipation, feeling sick (nausea) and feeling sleepy. Codeine is an opioid pain medication, sometimes called a narcotic. Acetaminophen is a less potent pain reliever that increases the effects of codeine. Codeine is an opioid agonist and therefore has abuse potential and a risk for fatal overdose from depressed respiration. Consumption of codeine with ethanol will result in additive central nervous system (CNS) and respiratory depressant effects. Tolerance. Over time, you may develop tolerance to the effects of codeine. This means your body needs more and more of the drug to feel the same pain relief or other desired effects. Learn about Fiorinal with Codeine (Butalbital Compound With Codeine) may treat, uses, dosage, side effects, drug interactions, warnings, patient labeling, reviews, and related medications. Learn about the potential side effects of codeine/promethazine. Includes common and rare side effects information for consumers and healthcare professionals. Codeine is a narcotic (opioid) drug used to relieve mild to moderately severe pain. Since codeine is a narcotic that is addictive and can cause serious side effects such as respiratory or cardiac arrest, and shock, which can lead to death. Dosages of codeine are tailored to each patient's needs. Each tablet contains 15, 30, or 60 mg of codeine sulfate and the following inactive ingredients: colloidal silicon dioxide, microcrystalline cellulose, pregelatinized starch, and stearic acid. For the Consumer. Applies to codeine: oral solution, oral tablet. Along with its needed effects, codeine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Codeine is an opiate pain medication that's sometimes referred to as a narcotic. Its active ingredient is found in many different medications that treat pain, cough, and diarrhea.