The level of consciousness is usually measured using the Glasgow coma score (GCS) or a modification of the GCS designed for assessing sedative drug overdose like the McCarron scale designed for assessment of barbiturate overdose. An even more simple scale is the 7 point scale shown on our admission form.

A GCS of 8 or less strongly suggests that the patient will not be capable of adequately protecting their airway and is likely to have a depressed cough reflex.

Patients who are drowsy or stuporous will often not require intubation provided they are nursed on their side, continue to be observed and no interventions are intended (appropriate for many benzodiazepine or alcohol overdoses for example)

The response to antagonists may be helpful in making a diagnosis in patients who are unconscious.

Patients ingesting theophylline and beta agonists who are not having seizures or arrhythmias will usually have a normal level of consciousness if no other drugs have been coingested.

Sedation occurs with chloral hydrate and MAO inhibitors.

Hallucinations and delirium may occur with cocaine and amphetamines.

TCAs, neuroleptics, antihistamines and carbamazepine cause greater degrees of sedation than drugs with a primary anticholinergic action.

A normal level of consciousness makes acidosis secondary to TCAs, cellular poisons (cyanide), CO, ethylene glycol, methanol, or isoniazid unlikely.

Most of these drugs cause CNS effects and sedation or seizures.

Arrhythmias occurring in an alert patient suggest adrenergic drugs such as theophylline, amphetamines or cocaine.

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Jennett B. Some aspects of prognosis after severe head injury. Scand J Rehabil Med 1972;4(1):16-20
Teasdale G, Jennett B. Assessment and prognosis of coma after head injury. Acta Neurochir (Wien) 1976;34(1-4):45-55
McCarron MM, Schulze BW, Walberg CB, Thompson GA, Ansari A. Short-acting barbiturate overdosage. Correlation of intoxication score with serum barbiturate concentration. JAMA 1982; 248(1):55-61.