Reinforcing and subjective effects of caffeine in normal human volunteers

Abstract

The reinforcing and subjective effects of caffeine (100 and 300 mg, PO) were determined in a group of 18 normal, healthy adults. Subjects (eight females, ten males) were light to moderate users of caffeine, and had no history of drug abuse. A discrete-trial choice procedure was used in which subjects were allowed to choose between the self-administration of color-coded capsules containing either placebo or caffeine. The number of times caffeine was chosen over placebo was used as the primary index of reinforcing efficacy. Subjective effects were measured before and several times after capsule ingestion. The low dose of caffeine was chosen on 42.6% of occasions, not significantly different from chance (50%). The high dose of caffeine was chosen on 38.9% of occasions, significantly less than expected by chance, indicating that this dose served as a punisher. Both doses of caffeine produced stimulant-like subjective effects, with aversive effects such as increased anxiety predominating after the high dose. When subjects were divided into groups of caffeine-sensitive choosers and nonchoosers, a consistent relationship emerged between caffeine choice and subjective effects; nonchoosers reported primarily aversive effects after caffeine (increased anxiety and dysphoria), whereas choosers reported stimulant and "positive" mood effects. When compared with previous findings, these results demonstrate that caffeine is less reinforcing than amphetamine and related psychomotor stimulants.

Association of the Anxiogenic and Alerting Effects of Caffeine with ADORA2A and ADORA1 Polymorphisms and Habitual Level of Caffeine Consumption

“…If 100 mg is around the 'threshold' dose for anxiety induction, then coffee is the only widely consumed caffeine-containing drink that would produce such an effectFalbeit a very modest effect in frequent caffeine consumers. Caffeine avoidance, predicted by caffeineinduced anxiety, is readily observed only at higher acute doses (300 mg) (Evans and Griffiths, 1992;Stern et al, 1989).…”

“…It is possible, for example, that the experience of increased anxiety after caffeine may cause vulnerable individuals to avoid caffeine subsequently (cf Evans and Griffiths, 1992;Stern et al, 1989), so that actually there are rather few such individuals among populations of frequent caffeine consumers. Indeed, even among infrequent consumers of caffeine a minority (19-29%) carry the rs5751876 TT genotype (Alsene et al, 2003;Childs et al, 2008).…”

Reinforcing Effects of Caffeine in Coffee and Capsules

“…Two subsequent studies extended these findings by using discrete-trial choice procedures to examine preferences between caffeine and placebo capsules in normal subjects with "usual" histories of caffeine use (Griffiths & Woodson, 1988b;Stern, Chait, & Johanson, 1989). In the first of these (Griffiths & Woodson, 1988b), forced exposure and choice opportunities occurred when subjects were abstinent overnight from their normal dietary caffeine intake.…”

“…The second study in normal subjects used a similar choice procedure in which subjects received four forced-exposure days (two each with caffeine and placebo) followed by three choice days (Stern et al, 1989). Unlike the previous study, forced exposure and choice opportunities were not scheduled to occur in a caffeineabstinent state.…”

“…More specifically, Experiment 1 used a variation on a concurrent-schedule choice procedure to elaborate knowledge about the reinforcing effects of caffeine by examining preference between capsules containing either caffeine or placebo. Unlike previous choice studies with caffeine in which a single choice opportunity occurred on each choice day Griffiths & Woodson, 1988b;Stern et al, 1989), the present experiment allowed multiple choice opportunities each day. Because previous research suggested that recent history of caffeine intake may be an important determinant of the reinforcing effects of caffeine (Griffiths & Woodson, 1988c), Experiment 1 examined preference for caffeine under conditions in which subjects had a recent history of heavy caffeine intake and in which subjects had been caffeine abstinent.…”