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The Coke and Pepsi brain-scan study and the Pepsi paradox

Academic researchers ran taste tests and brain scans with Coca-Cola and Pepsi, with and without brand cues. Brand knowledge changed stated preference and brain responses. The brands were stimuli. The funding statements read name a foundation and US health agencies, not either company.

2004. Marks publication of McClure and colleagues in Neuron (volume 44, issue 2). A follow-up with brain-damaged patients appeared in 2008. Chronology section: 1990 to 2009.

StudyIndependent experimentNeuroConsumer

Where it sits
Academic psychologyResearch published for other researchers and students.
Evidence level
Independent experimentIndependent research, with its design and limits stated.
Organizations
Coca-Cola, PepsiAn organization is listed where the sources concern it. The text says exactly how.
Sources inspected
4 of 42 with the relevant text, company document or archive item checked, 2 as an abstract or reference article, 0 not verified.

What happened

In 2004 McClure and colleagues published a study in Neuron in which volunteers took part in taste tests and fMRI experiments with Coca-Cola and Pepsi, delivered either anonymously or with a brand cue. In 2008 Koenigs and Tranel ran taste tests with brain-damaged patients and healthy adults to ask how damage to the ventromedial prefrontal cortex affects brand-cued preference.

The psychological idea

The 2004 abstract notes that the two colas are nearly identical in chemical composition, yet people often strongly prefer one. The design separates two inputs to preference: the taste itself, delivered anonymously, and knowledge of the brand, delivered through a cue. Later authors use the term Pepsi paradox for a consistent preference for Coca-Cola when the brand is visible but none when brands are hidden.

In practice

No company practice is documented in these papers. In the 2004 abstract, activity in the ventromedial prefrontal cortex correlated with stated preference under anonymous delivery, and brand knowledge strongly affected both stated preference and brain responses. A reprinted press release reports 67 volunteers and a brand effect for Coke but not Pepsi. In 2008, 44 people took part. Healthy adults chose the labeled cup 60 percent of the time in Coke trials, while patients with ventromedial lesions chose it 71 percent of the time in Pepsi trials.

Why it mattered

The study became a standard example in early neuromarketing and in teaching about how brand knowledge shapes experience. It showed in a controlled design that a label can alter reported preference for a nearly identical product.

Limits and qualifications

Only the abstract and publisher record of the 2004 paper could be read, so its sample is known here from a reprinted press release. The 2004 funding line names a foundation and a US health agency grant. The 2008 acknowledgements name two US public grants, and its conflict statement reads none declared. No source read shows that Coca-Cola or Pepsi commissioned, funded or took part in either study. Brain activity does not show why a person prefers a drink, and the samples are small.

Evidence behind the claims

  • McClure and colleagues (Neuron, 2004) ran taste tests and fMRI experiments with Coca-Cola and Pepsi under anonymous and brand-cued delivery; in the anonymous condition ventromedial prefrontal cortex activity correlated with stated preference, and in the brand-cued condition brand knowledge strongly affected stated preference and brain responses.

    Experimental findingSource: [1]Where: AbstractChecked at abstract level

  • A reprinted press release on the 2004 study reports 67 volunteers, and says knowing a drink was Coke shifted preference and activated the dorsolateral prefrontal cortex and hippocampus while Pepsi brand knowledge had no influence.

    DocumentedSource: [2]Where: Press-release textChecked at page level

  • The 2004 paper's record states support from the Kane Family Foundation and NIDA grant DA-11723 and names no company as funder.

    DocumentedSource: [1]Where: Funding statement on the publisher recordChecked at abstract level

  • Koenigs and Tranel (2008) tested 44 people: 12 with ventromedial prefrontal lesions, 16 with lesions elsewhere and 16 healthy adults.

    Experimental findingSource: [3]Where: Methods, participants

  • In blind tests Pepsi was chosen 55, 57 and 63 percent of the time by the healthy, other-lesion and ventromedial-lesion groups. In semi-blind trials with the same cola in both cups, one labeled, healthy adults chose the labeled cup 60 percent of the time in Coke trials and 54 percent in Pepsi trials, while the ventromedial group chose it 39 percent in Coke trials and 71 percent in Pepsi trials.

    Experimental findingSource: [3]Where: Methods (semi-blind design) and Results

  • The Koenigs and Tranel paper states support from NINDS P01 NS19632 and NIDA R01 DA022549, declares no conflict of interest, and names no company as funder or supplier.

    DocumentedSource: [3]Where: Acknowledgements and conflict of interest statement

  • Kühn and Gallinat (2013) attribute the Pepsi paradox to McClure and colleagues and describe it as a consistent preference for Coca-Cola when brand information is visible but none when brands are hidden.

    DocumentedSource: [4]Where: Introduction as returned by the fetch tool

People involved

  • Samuel M. McClure. Lead author, 2004 Neuron study
  • P. Read Montague. Senior author, 2004 Neuron study
  • Michael Koenigs. Lead author, 2008 lesion study
  • Daniel Tranel. Senior author, 2008 lesion study

In the Psy101 course

This is course relevance only. It is not evidence for the historical or corporate claims on this page.See the full course map.

Sources and inspection

4 of 4 sources were opened and read at the level shown. A source marked as not verified supports no claim on this page by itself.

  1. [1]
    Neural correlates of behavioral preference for culturally familiar drinksMcClure, S; Li, J; Tomlin, D; Cypert, K; Montague, L; Montague, P. Neuron (record held by Arizona State University research portal), 2004. Journal article. Primary source.Abstract or publisher record onlyRead the publisher record as returned by the fetch tool: summary of the abstract, authors, citation and the funding and acknowledgement text. The full Neuron paper was not read.
  2. [2]
    Coke versus Pepsi: It's all in the headinnovations-report.com (press release reprint). innovations-report.com, 2004. News report. Secondary account.Reference article readRead a reprinted press release (a secondary news account, not company material; reference-page is the nearest allowed level). It gives 67 volunteers, brain regions and the Coke versus Pepsi contrast, and has no funding statement.
  3. [3]
    Prefrontal cortex damage abolishes brand-cued changes in cola preferenceKoenigs, M; Tranel, D. Social Cognitive and Affective Neuroscience (author manuscript, PubMed Central), 2008. Journal article. Primary source.Relevant text checkedRead the author manuscript as returned by the fetch tool: participants, semi-blind design, choice percentages, acknowledgements and conflict statement. Did not read every section.
  4. [4]
    Does Taste Matter? How Anticipation of Cola Brands Influences Gustatory Processing in the BrainKühn, S; Gallinat, J. PLoS One (PubMed Central), 2013. Journal article. Critique or replication.Relevant text checkedRead the introduction passages as returned by the fetch tool that cite McClure 2004 and describe the Pepsi paradox. Used only for how a later paper defines the term.

Access note: The full 2004 Neuron paper was not opened. Its participant number rests on a reprinted press release.

Independent source review: Claude review agent, independent of the research agent, 2026-10-21. Verdict: pass-with-edits.