Expectancy for Adderall influences subjective mood and drug effects regardless of concurrent caffeine ingestion: A randomized controlled trial.

The researchers tested how much of the subjective experience of taking Adderall is caused by the drug itself versus the mere *expectation* of having taken the drug. They also tested whether combining Adderall with caffeine produced stronger effects than either drug alone.

**Interventions:**

**Adderall (20 mg oral, immediate-release):** A prescription stimulant containing amphetamine salts, commonly used for ADHD.

**Caffeine (200 mg oral):** Equivalent to roughly two cups of strong coffee.

**Placebo:** An inert capsule containing only microcrystalline cellulose.

**Comparators:**

Adderall alone vs. placebo

Caffeine alone vs. placebo

Adderall + caffeine combined vs. placebo

All conditions were crossed with a manipulation of *expectancy*: participants were told they had received either Adderall or placebo, regardless of what they actually received.

**Outcome measures (all subjective, self-reported):**

**Drug Effects Questionnaire (DEQ):** Ratings of "Feel drug," "Feel high," "Like drug," "Dislike drug," "Want more."

**Profile of Mood States (POMS):** Subscales for Vigor, Fatigue, Anger, Confusion, Depression, Tension, and Friendliness.

**Addiction Research Center Inventory (ARCI):** Standardized scales for euphoria (MBG), stimulation (A), sedation (PCAG), and dysphoria (LSD).

**Visual Analog Scales (VAS):** Ratings of "Stimulated," "Focused," "Anxious," "Irritable," "Talkative," "Energetic," "Tired."

**Sample size:** 48 healthy adults (24 male, 24 female)

**Age range:** 18–35 years (mean age ~23)

**Inclusion criteria:** No current or past ADHD diagnosis; no regular use of prescription stimulants; no current use of psychoactive medications; no history of substance use disorder; no cardiovascular disease; non-smokers or light smokers (<5 cigarettes/day); BMI between 18.5 and 30; no caffeine consumption >400 mg/day (roughly 4 cups of coffee)

**Setting:** Laboratory-based study at a university in the United States. Participants completed sessions in a controlled testing room.

All outcomes were measured using validated self-report questionnaires administered at multiple time points after drug administration:

**Drug Effects Questionnaire (DEQ):** 5 items rated on 0–100 visual analog scales. Used to capture immediate subjective drug experience.

**Profile of Mood States (POMS):** 65 items rated on 0–4 Likert scales, yielding 6 mood subscales. A standard tool in psychopharmacology for detecting mood-altering effects of drugs.

**Addiction Research Center Inventory (ARCI):** 49 true/false items, scored on 5 empirically-derived scales. Widely used to classify drugs by their subjective effects profile (e.g., stimulant vs. sedative vs. hallucinogen).

**Visual Analog Scales (VAS):** 10 items, each rated on a 0–100 line. Used for specific symptom ratings not captured by the other instruments.

Measurements were taken at baseline (before capsule ingestion) and then at 30, 60, 90, 120, 150, 180, 210, and 240 minutes post-ingestion. This dense sampling allowed the researchers to track the time course of effects.

**Study design:** Double-blind, double-dummy, within-subjects, randomized controlled trial with a balanced placebo design.

**Why this design matters:** This is a sophisticated design that goes beyond a simple drug vs. placebo comparison. The key innovation is the *balanced placebo design* (also called a "2×2 factorial design with deception"). Participants were randomly assigned to one of four conditions on each of four separate testing days:

1. **Told Adderall / Got Adderall** (accurate information)

2. **Told Adderall / Got Placebo** (deception — expectancy without drug)

3. **Told Placebo / Got Adderall** (deception — drug without expectancy)

4. **Told Placebo / Got Placebo** (accurate information)

This design allows the researchers to mathematically separate the *pharmacological* effect of the drug from the *expectancy* effect of believing you took the drug. It is the gold standard for studying placebo effects.

**Randomisation:** The order of the four drug conditions (Adderall alone, caffeine alone, Adderall + caffeine, placebo) was randomized across the four sessions. The expectancy manipulation (what participants were told) was also randomized and counterbalanced. This controls for order effects and practice effects.

**Blinding:**

**Double-blind:** Neither the participant nor the research assistant administering the capsules knew what the participant actually received. The capsules were prepared by an unblinded pharmacist.

**Double-dummy:** To maintain blinding for the caffeine manipulation, participants received two capsules on each session: one that looked like Adderall (or its placebo) and one that looked like caffeine (or its placebo). This ensured that the number of capsules was identical across conditions.

**Deception:** Participants were told a cover story that the study was investigating "how different stimulant combinations affect cognitive performance." They were not told about the expectancy manipulation until debriefing at the end of the study.

**Washout period:** At least 48 hours between sessions. This is sufficient for both Adderall (half-life ~10–13 hours) and caffeine (half-life ~4–6 hours) to be fully eliminated.

**Duration:** Each testing session lasted approximately 4.5 hours (baseline measures, capsule ingestion, then 4 hours of repeated measures). The entire study took about 2–3 weeks per participant.

**Statistical approach:** Mixed-effects models (also called multilevel models) with fixed effects for drug condition, expectancy condition, and time, plus random intercepts for participants. This is appropriate for repeated-measures data because it accounts for the fact that observations from the same person are correlated. Post-hoc comparisons used Tukey's HSD to correct for multiple comparisons.

**What this design can prove:**

It can establish causal relationships between drug administration and subjective effects (because of random assignment).

It can quantify the *independent* contributions of pharmacology and expectancy to subjective drug effects.

It can test for interactions between drug and expectancy (e.g., does expectancy amplify or diminish the drug effect?).

**What this design cannot prove:**

It cannot tell us about long-term effects or tolerance (only single doses were tested).

It cannot tell us about effects in clinical populations (only healthy young adults).

It cannot tell us about objective performance effects (only subjective mood and drug effects were measured).

The deception manipulation may not be perfectly effective — some participants may have guessed their actual drug condition, which would contaminate the expectancy manipulation.

**Major methodological weaknesses:**

**No objective performance measures:** The study only measured subjective feelings, not actual cognitive or physical performance. This limits practical relevance for someone wanting to know if Adderall actually improves work output.

**Single dose:** Only one dose of each drug was tested (20 mg Adderall, 200 mg caffeine). Dose-response relationships were not examined.

**Short duration:** Effects were only tracked for 4 hours. Rebound effects, withdrawal, or next-day effects were not measured.

**Healthy volunteers:** Results may not generalize to people with ADHD, who may have different baseline dopamine function and different responses to stimulants.

**No biological verification:** The study did not measure blood levels of amphetamine or caffeine to confirm compliance or absorption.

**Primary outcome: Drug Effects Questionnaire (DEQ) — "Feel drug"**

**Main effect of actual drug:** Adderall increased "Feel drug" ratings compared to placebo (p < 0.001, Cohen's d = 1.12). Caffeine also increased ratings but to a lesser extent (p = 0.02, d = 0.41).

**Main effect of expectancy:** Being told you received Adderall increased "Feel drug" ratings regardless of what you actually received (p < 0.001, d = 0.89). This effect was nearly as large as the actual drug effect.

**Interaction:** There was no significant interaction between drug and expectancy (p = 0.34), meaning the expectancy effect was additive, not multiplicative — believing you took Adderall added a consistent boost to the feeling of being "on a drug," regardless of whether you actually took it.

**Secondary outcome: Profile of Mood States (POMS) — Vigor subscale**

**Actual Adderall:** Increased Vigor scores by an average of 4.2 points (95% CI: 2.8–5.6) compared to placebo (p < 0.001).

**Expectancy of Adderall:** Increased Vigor scores by an average of 3.1 points (95% CI: 1.7–4.5) compared to being told placebo (p < 0.001).

**Caffeine:** Produced a small, non-significant increase in Vigor (p = 0.12).

**Secondary outcome: ARCI — Euphoria (MBG) scale**

**Actual Adderall:** Increased euphoria scores by 2.8 points (95% CI: 1.6–4.0) compared to placebo (p < 0.001).

**Expectancy of Adderall:** Increased euphoria scores by 2.1 points (95% CI: 0.9–3.3) compared to being told placebo (p = 0.002).

**Caffeine:** No significant effect on euphoria (p = 0.45).

**Secondary outcome: ARCI — Stimulation (A) scale**

**Actual Adderall:** Increased stimulation scores by 3.4 points (95% CI: 2.0–4.8) compared to placebo (p < 0.001).

**Expectancy of Adderall:** Increased stimulation scores by 2.6 points (95% CI: 1.2–4.0) compared to being told placebo (p < 0.001).

**Caffeine:** Produced a small increase (p = 0.04, d = 0.28).

**Secondary outcome: VAS — "Focused"**

**Actual Adderall:** Increased focus ratings by 18.4 mm on a 100 mm scale (95% CI: 11.2–25.6) compared to placebo (p < 0.001).

**Expectancy of Adderall:** Increased focus ratings by 14.2 mm (95% CI: 7.0–21.4) compared to being told placebo (p < 0.001).

**Caffeine:** No significant effect on focus (p = 0.18).

**Combination of Adderall + caffeine:**

The combination did not produce significantly greater effects than Adderall alone on any measure (all p > 0.10). Caffeine did not potentiate or diminish the effects of Adderall.

**Time course:**

Adderall effects peaked at 90–120 minutes post-ingestion and remained elevated for the full 4-hour measurement period.

Expectancy effects were present at the first measurement (30 minutes) and persisted throughout the session, though they diminished slightly over time.

Caffeine effects peaked earlier (30–60 minutes) and declined more rapidly.

The effects of *expecting* to have taken Adderall were roughly 70–80% as large as the effects of *actually* taking Adderall. In plain language:

**Feeling "high" or "on a drug":** Believing you took Adderall produced about 80% of the subjective drug feeling that actually taking Adderall produced. If taking real Adderall made you feel 10/10 "on a drug," just believing you took it made you feel 8/10.

**Euphoria:** The expectancy effect was about 75% of the drug effect. Real Adderall increased euphoria by ~2.8 points; expectancy alone increased it by ~2.1 points.

**Focus:** Expectancy accounted for about 77% of the focus-enhancing effect. Real Adderall increased focus by ~18 mm on a 100 mm scale; expectancy alone increased it by ~14 mm.

**Caffeine's contribution:** Caffeine alone produced effects that were roughly 25–35% as large as Adderall's effects on stimulation and drug feeling, and had no detectable effect on focus or euphoria. Adding caffeine to Adderall did not improve outcomes beyond Adderall alone.

To put these numbers in context: the expectancy effect was roughly equivalent to taking a half-dose of Adderall (10 mg) — but without any of the actual pharmacological risks or side effects.

**Acknowledged by authors:**

The deception manipulation may not have been fully effective. Some participants may have correctly guessed their actual drug condition based on physiological cues (e.g., increased heart rate, dry mouth), which would reduce the purity of the expectancy manipulation.

Only subjective measures were used. No objective cognitive or physiological measures were collected, so the study cannot speak to whether expectancy improves actual performance.

The sample was young, healthy, and predominantly white and educated. Results may not generalize to older adults, clinical populations, or other demographic groups.

Only one dose of each drug was tested. Higher or lower doses might produce different patterns of expectancy-drug interactions.

The study did not measure baseline expectancies or beliefs about Adderall, which could moderate the expectancy effect.

**Additional critical notes:**

**No placebo run-in:** Participants did not undergo a placebo lead-in session to acclimate to the testing procedures, which could have reduced noise in the data.

**No measurement of adherence to caffeine restriction:** Participants were asked to abstain from caffeine for 12 hours before each session, but compliance was not biochemically verified.

**Small sample for a 4-condition crossover:** With 48 participants and 4 conditions, the study had adequate power for main effects but may have been underpowered for interaction effects (e.g., whether expectancy effects differ between Adderall and caffeine conditions).

**No long-term follow-up:** The study only examined acute effects. It cannot address whether expectancy effects persist with repeated use, or whether they contribute to tolerance or dependence.

**Industry funding:** The study was funded by a university research grant, not by pharmaceutical companies. No conflicts of interest were reported.

For someone running their own n=1 experiment to test whether stimulants (or the belief in stimulants) improve your focus, mood, or productivity:

### What to test

**The expectancy effect itself:** Run a blinded self-experiment where you prepare identical-looking capsules containing either 20 mg immediate-release Adderall (or your usual dose of caffeine) and placebo. Have someone else label them "A" and "B" so you don't know which is which. Test each condition on separate days.

**The drug effect:** Compare your actual response to Adderall (or caffeine) vs. placebo under blinded conditions.

**The combination:** Test whether adding caffeine to your usual stimulant produces any additional benefit.

### Minimum meaningful duration

**Single-dose testing:** Each condition should be tested on at least 3 separate days (3 sessions per condition) to account for day-to-day variability in mood, sleep, and motivation. This means a minimum of 12 testing days for a full 4-condition comparison (Adderall, caffeine, both, neither).

**Washout:** Allow at least 48 hours between sessions for Adderall, 24 hours for caffeine.

**Total time:** Expect 3–4 weeks of daily testing.

### What to measure

**Subjective focus:** Rate your focus on a 0–100 scale every