Mortalities due to codeine appear to be quite unusual. Most frequently observed adverse effects referable to acetaminophen include lightheadedness, dizziness, sedation, nausea and vomiting. These effects seem to be more prominent in ambulatory than in nonambulatory patients and some of these adverse reactions may be alleviated if the patient lies down. Other adverse reactions include euphoria, dysphoria, constipation and pruritus. Rare hypersensitivity reactions may occur that require discontinuation of the drug.
Hypersensitivity is manifested by rash or urticaria.
Regular use of acetaminophen has shown to produce a slight increase in prothrombin time in patients receiving oral anticoagulants, but the clinical significance of this effect is not clear. The incidence of gastrointestinal upset is less than after salicylate administration. Patients suffering from an overdose of acetaminophen will progress through 3 stages if untreated. During the first stage, which lasts from 12 to 24 hours, there may be anorexia, nausea, vomiting, diaphoresis and pallor. After 24 hours, earlier symptoms tend to abate and the patient may even feel well for one or a few days.