Low-dose caffeine discrimination and self-reported mood effects in normal volunteers.
Discrimination training can reliably detect and produce mood effects from caffeine doses as low as 18 mg—far below typical behavioral thresholds.
01Research in Context
What this study did
Six adults with no drug problems came to a lab. They got pills that held 0, 10, 18, or 32 mg of caffeine.
After each pill they pressed one key if they felt caffeine, another if they felt nothing. They also filled out a short mood form. The team paid them for correct choices.
What they found
Everyone learned to call 18 mg correctly. One person even caught 10 mg. At 32 mg they were perfect.
The same tiny doses lifted alertness and calm on the mood form. So behavior plus self-report tracked doses far below a cup of coffee.
How this fits with other research
Rasing et al. (1992) used the same lab set-up. They tied a drug feeling to colored lights through equivalence training. Together the papers show drug cues can enter larger stimulus classes.
Jenkins et al. (1973) also worked with near-threshold signals. They found error latencies stretched when light differences shrank. K et al. now show the same fine control with an internal drug cue.
Rojahn et al. (1994) blended tiny ethanol and cocaine doses that did nothing alone. Their combo lowered brain-reward thresholds. K et al. prove a single low drug can still be caught if you sharpen the measure.
Why it matters
Your clients may take meds, supplements, or energy drinks. This study says people can feel, report, and discriminate micro-doses once you give clear feedback. Try adding a quick self-rating scale after PRN meds. You might spot side effects sooner and adjust doses before problem behavior shows up.
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02At a glance
03Original abstract
A caffeine versus placebo discrimination procedure was used to determine the lowest caffeine dose that could produce discrimination and self-reported mood effects in normal volunteers. During daily sessions under double-blind conditions, caffeine-abstinent subjects orally ingested a capsule containing 178 mg caffeine or placebo. Before beginning discrimination training, the compounds were identified to subjects by letter codes. Fifteen, 30, and 45 min after capsule ingestion, subjects guessed the capsule's letter code. Correct guesses at 45 min earned money. After each session, subjects received a supplementary capsule containing caffeine or placebo to ensure that, within each phase of the study, subjects received the same daily dose of caffeine equal to the training dose. Five of the 15 subjects acquired the caffeine versus placebo discrimination within the first 20 sessions (greater than or equal to 75% correct); 6 other subjects acquired the discrimination with additional training. Nine subjects who acquired the discrimination were subsequently trained at progressively lower caffeine doses. In general, the lowest dose to produce discrimination (greater than or equal to 75% correct) was also the lowest dose to produce self-reported mood effects: 4 subjects showed discrimination and self-reported mood effects at 100 mg caffeine, 2 at 56 mg, 1 at 32 mg, and 1 at 18 mg. One of these subjects also showed self-reported mood effects at 10 mg. The present study documents discriminative stimulus and self-reported mood effects of caffeine at doses below those previously shown to affect any behavior in normal volunteers.
Journal of the experimental analysis of behavior, 1992 · doi:10.1901/jeab.1992.57-91