Opiates and opioids apparently work through specific receptors in the central nervous system. Aspirin and the other nonprescription drugs are thought to work by blocking the body's production of particular types of prostaglandins, hormone-like substances that are produced throughout the body. This can be minimized by taking them with meals or milk. Acetaminophen does not cause as many intestinal side effects as aspirin, but it should be used with caution by persons who have liver or kidney disorders. The combination of aspirin and acetaminophen is especially damaging to the kidneys, as is heavy alcohol consumption and long-term acetaminophen use is damaging to the liver.
Codeine often causes nausea, dizziness, and constipation.
A more serious problem, however, involves the tendency of codeine and other narcotic drugs to produce drowsiness. Thus, these agents should not be taken by anyone who must remain alert. In addition, narcotic painkillers should never be taken in combination with alcoholic beverages, antihistamines, other allergy or cold pills, anticonvulsants, tranquilizers, muscle relaxants, or any other substance that depresses the central nervous system. Narcotics increase the effects of these drugs on the brain, and a fatal overdose can result from their combined use. The potentially addictive effect of opiates and other narcotic agents is the major drawback to their long-term use.