Overdosage with codeine can cause transient euphoria, drowsiness, dizziness, weariness, diminution of sensibility, loss of sensation, vomiting, transient excitement in children and occasionally in adult women, miosis progressing to nonreactive pinpoint pupils, itching sometimes with skin rashes and urticaria, and clammy skin with mottled cyanosis. In more severe cases, muscular relaxation with depressed or absent superficial and deep reflexes and a positive Babinski sign may appear. Marked slowing of the respiratory rate with inadequate pulmonary ventilation and consequent cyanosis may occur. Terminal signs include shock, pulmonary edema, hypostatic or aspiration pneumonia and respiratory arrest, with death occurring within 6 to 12 hours following ingestion. Overdoses of antihistamines may cause hallucinations, convulsions, or possibly death, especially in infants and children.
Antihistamines are more likely to cause dizziness, sedation and hypotension in elderly patients.
Overdosage with pseudoephedrine can cause excessive CNS stimulation resulting in excitement, nervousness, anxiety, tremor, restlessness and insomnia. Other effects include tachycardia, hypertension, pallor, mydriasis, hyperglycemia and urinary retention. Severe overdosage may cause tachypnea or hyperpnea, hallucinations, convulsions or delirium, but in some individuals there may be CNS depression with somnolence, stupor or respiratory depression. Severe hypokalemia can occur, probably due to compartmental shift rather than depletion of potassium. No organ damage or significant metabolic derangement is associated with pseudoephedrine overdosage.