Ketamine anaesthetic and sedative drug, molecular model. Ketamine is a sedative, anaesthetic, antidepressant, and pain reliever. Ketamine is preferred for patients with compromised airway passages because it suppresses breathing less than other anaesthetics. The ketamine structure shown here is the R enantiomer, but the drug is administered as a racemic mixture. Atoms are colour-coded: carbon is black; hydrogen is white; chlorine is green; nitrogen is blue; oxygen is red