Orally delivered cocaine as a reinforcer for rhesus monkeys.

Orally delivered cocaine was established as a reinforcer for six rhesus monkeys. Cocaine and its vehicle, water, were available from separate spouts under independent concurrent fixed-ratio schedules. The positions of cocaine and water were reversed between spouts from session to session. Cocaine consistently maintained higher response rates than water. Cocaine concentration was systematically varied for three of the six monkeys tested, and cocaine intake (mg of drug/kg of body wt.) increased with increases in drug concentration.