Table 1.

Commonly used drug self-administration procedures

Procedure	Advantages	Disadvantages
Free access   Participants request drug (most often verbally) whenever theywant it     Dependent measures: number of doses chosen, interval between dose requests	Simple Somewhat naturalistic for some drugs, such as coffee or cigarettes	Can be insensitive to dose conditions Most drugs of abuse are not available in unlimited supply, and are not safe to deliver in this manner
Choice (discrete trial choice)   Participants perform a verbal or nonverbal operant to select between two potential reinforcers (drug vs. drug, drug vs. placebo, drug vs. money)     Dependent measures: number or percentage of drug chosen in comparison with alternative reinforcers	Simple Experimenter controls the interval at which doses are available Enhanced safety It is possible to test the relative reinforcing effects of two or more different drugs	Requires many sessions to examine dose– response relationships The appropriate alternative money amount may vary for different populations
Multiple-choice procedure   Participants are asked to make a series of choices between the drug under investigation and other reinforcers of increasing monetary value or monetary values that escalate     Dependent measure: the monetary value at which participants switch from choosing drug to choosing money (crossover point)	Does not require multiple-drug administrations Sensitive to dose manipulations	Not all choices are reinforced There is often considerable delay between the time the choice is made and when the reinforcer is given Generally not considered a direct measure of a drug’s reinforcing effects
Fixed-ratio operant procedure   Participants are given the opportunity to ‘work’ for the drug under investigation by responding on a manipulandum a fixed number of times     Dependent measures: amount of drug consumed or rate of responding	This procedure is similar to that used in a large number of preclinical studies, which allows for indirect comparisons across species	Depending on the dose, drug, and ratio requirement, it is sometimes difficult to differentiate the reinforcing effects of different doses Results can vary depending on the fixed-ratio value chosen, so an ‘appropriate’ fixed-ratio value can be difficult to determine
Progressive-ratio operant procedure   Participants are given the opportunity to ‘work’ for a drug by responding on a manipulandum; the ratio requirement increases after each drug delivery     Dependent measures: amount of drug consumed, rate of responding, maximum ratio value completed (break point)	Provides a dependent measure that allows for direct comparison across different drugs Sensitive to dose manipulations Amenable to a behavioral economic analysis, which generates a rich array of dependent measures	If shorter intertrial intervals are used, carryover effects from one dose to another can interfere with the ability to perform the operant If longer intertrial intervals are used to minimize carryover effects, the study duration can become prohibitively long