Introduction to Psychology
Popular Psychology

Back to the directoryFind in the timeline

Hollingworth's caffeine study for Coca-Cola and the Chattanooga trial

The Coca-Cola Company's attorneys hired Harry Hollingworth to test caffeine on 16 volunteers for the 1911 Chattanooga trial. The company financed the placebo-controlled, blinded 40-day study, which reported a genuine stimulant effect. It did not settle the legal question.

March 1911. Month the Chattanooga trial began, per the British Psychological Society article. The experiments were run in the weeks before, and Hollingworth's monograph appeared in 1912. Chronology section: 1880 to 1919.

StudyDocumentedConsumerDesign ethics

Where it sits
Academic psychologyResearch published for other researchers and students.
Evidence level
DocumentedThe event or practice is documented by primary or authoritative sources.
Organizations
Coca-ColaAn 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 March 1911 the US government's case against the Coca-Cola Company, later known as United States v. Forty Barrels and Twenty Kegs of Coca-Cola, went to trial in Chattanooga. The company's attorneys needed human data on caffeine. According to a British Psychological Society article, James McKeen Cattell and others declined before Harry Hollingworth, a Barnard College instructor, accepted. His studies took 40 days, and he testified for the defense in the third week of the trial.

The psychological idea

The study compared caffeine with a placebo of capsules of sugar of milk. Sixteen subjects, ten men and six women, were engaged full time for 40 days. Neither the subjects nor the assistants recording results knew whether a measurement was a caffeine or a control record. Doses ran from one to six grains. Tests included color naming, calculation, choice reaction, steadiness and tapping. A final week compared soda fountain syrup with and without caffeine.

In practice

Hollingworth concluded that caffeine had a genuine drug effect, not merely excitement or interest. Effects on motor processes came quickly and were transient. Effects on higher mental processes came more slowly and lasted longer. He reported no secondary depression. Six-grain doses impaired sleep in most subjects, while one to four grains did so only in a few. At trial he said Coca-Cola appeared to be a mild stimulant and showed none of the harm the government alleged.

Why it mattered

A psychologist's controlled experiment was put to a court as defense evidence. The Chattanooga judge agreed that caffeine was an inherent ingredient and dismissed the suit before it reached a jury. On 22 May 1916 the US Supreme Court held caffeine an added ingredient, reversed the judgment and remanded the case, saying that whether it was harmful was a question of fact for a jury.

Limits and qualifications

The Coca-Cola Company financed the experiments, and a later appropriation paid for publication. Hollingworth says writing up the results was his own initiative. Sixteen subjects is a small sample, and he states that the results cannot be carried over to continuous use of the drug. The courts did not rule on caffeine's safety. The sources read do not describe consent procedures, so informed consent and participant welfare cannot be judged from them.

Evidence behind the claims

  • Attorneys for the Coca-Cola Company sought human data for the Chattanooga trial; James McKeen Cattell and others declined before Harry Hollingworth, a Barnard College instructor, accepted; the studies were completed in 40 days and the trial began in March 1911.

    DocumentedSources: [2] [3]Where: Opening sections of both articlesChecked at page level

  • The Coca-Cola Company of Atlanta financed the experiments and a later appropriation paid for publication; Hollingworth says preparing the results for publication was his own contribution, undertaken on his own initiative.

    Company self-reportSource: [1]Where: Preface

  • Sixteen subjects, ten men and six women, were engaged full time for 40 days; sugar of milk capsules were the control; no assistant knew whether a measurement was a caffeine or control record; doses ran from one to six grains; tests included color naming, opposites, calculation, cancellation, choice reaction, steadiness, tapping and the three-hole test; a final week used syrup with and without caffeine.

    Experimental findingSource: [1]Where: Preface and early methods chapters

  • Hollingworth concluded that the effect on motor processes comes quickly and is transient, the effect on higher mental processes comes more slowly and is more persistent, with no secondary depression, and that the result is a genuine drug effect and not merely excitement or interest; smaller doses (one to four grains) did not produce appreciable sleep disturbance except in a few cases, while six grains marked sleep impairment in most subjects.

    Experimental findingSource: [1]Where: Chapter XV conclusions; Chapter XIII sleep summary

  • Hollingworth states that the results cannot be carried over bodily to the question of the continuous use of the drug.

    Experimental findingSource: [1]Where: Chapter XV, conclusions

  • Hollingworth testified in the third week of the trial and said Coca-Cola appeared a mild stimulant without the harm alleged; the judge held caffeine an inherent ingredient and the suit was dismissed without reaching the jury; the company later paid costs and reduced the caffeine content.

    DocumentedSource: [2]Where: Sections on the trial and its endingChecked at page level

  • On 22 May 1916 the US Supreme Court held caffeine an added ingredient, reversed the judgment and remanded the case, and held that whether caffeine was deleterious was a question of fact for the jury.

    DocumentedSource: [4]Where: 241 U.S. 265, opinion text

People involved

  • Harry L. Hollingworth. Experimenter and defence witness
  • James McKeen Cattell. Psychologist who declined the commission, per the British Psychological Society article

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]
    The Influence of Caffein on Mental and Motor EfficiencyHollingworth, H. L.. Science Press, New York (Archives of Psychology and Columbia Contributions series); scan at Internet Archive, 1912. Journal article. Primary source.Relevant text checkedRead the scan text as returned by the fetch tool in three windows: the preface and methods, a later window with the chapter on sleep, and the final window with the Chapter XV conclusions. The middle chapters were not read in full. The title page is missing from the scan, and the 1912 date comes from other catalog records of the same title.
  2. [2]
    Coca-Cola: brain tonic or poison?British Psychological Society, The Psychologist. The Psychologist, British Psychological Society, Undated. News report. Secondary account.Reference article readRead the magazine article as returned by the fetch tool. It gives who commissioned the study, who declined, the 40 days, the March 1911 trial start, the testimony, the dismissal, the 1916 ruling in outline and the settlement. No author or year was shown.
  3. [3]
    A Century Later, Jury's Still Out on Caffeine LimitsHistory News Network. History News Network, Undated. News report. Secondary account.Reference article readRead the article as returned by the fetch tool. It says the company hired Hollingworth, an instructor at Barnard College, and gives 16 subjects and a double-blind design. It reports neither results nor the verdict.
  4. [4]
    United States v. Forty Barrels and Twenty Kegs of Coca-Cola, 241 U.S. 265Supreme Court of the United States. Legal Information Institute, Cornell Law School, 1916. Legal or regulatory text. Primary source.Relevant text checkedRead the 1916 opinion page as returned by the fetch tool: decision date, the holding that caffeine is an added ingredient, the jury question and the reversal and remand. The opinion does not describe the experiments.

Access note: Benjamin, Rogers and Rosenbaum (1991) was not opened and no trial transcript was read. The two news articles show no publication year. Whether Hollingworth was paid personally was not found in the pages read.

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