1. among humans, the taking of a medication (e.g., injecting insulin) or an abused substance (e.g., injecting heroin, inhaling cannabis) by the individual himself or herself.

2. in nonhuman animal research, a procedure used to study the rewarding effects of drugs. Animals (usually primates or rodents) are required to perform an operant response (e.g., lever pressing) to receive a drug infusion, which is delivered via an intravenous catheter or through a cannula implanted in the brain. Also called drug self-administration.