Answer: In a randomized, double-blind four-condition crossover study of 28 healthy adults, researchers deliberately adjusted alcohol doses for men and women to obtain similar measured breath alcohol concentrations. The study did not demonstrate a statistically significant difference between the enrolled men and women on its laboratory tracking and psychomotor-vigilance outcomes. Women nevertheless reported greater alcohol-related drunkenness and sedation on particular subjective measures. Adding an energy drink improved some test scores relative to alcohol alone, but did not eliminate alcohol-related effects or establish that anyone could drive safely. These are distinct findings: a breath reading is not a direct venous whole-blood assay, a feeling is not a driving test, and a computerized task is not a crash reconstruction.
The underlying original experiment is Hladun and colleagues’ 2025 Frontiers in Pharmacology article, “No significant gender differences in driving-related skills following alcohol mixed with energy drinks during an experimental binge-drinking episode”. Its most useful forensic lesson is how to separate comparable measured exposure, subjective responses, selected psychomotor outcomes, and the limits of extrapolation to one individual.
What question did the investigators actually test?
Many claims about alcohol and energy drinks bundle three different propositions: that women and men achieve different alcohol concentrations after the same drink, that they feel alcohol differently, and that they perform differently at similar concentrations. Those propositions require different measurements. This study focused on comparing alcohol-plus-energy-drink effects between men and women when administered doses were chosen to bring measured alcohol and caffeine exposures closer together.
The investigators tested driving-related skills with computer-based psychomotor and visuomotor tasks, and also collected self-reported intoxication, sedation, perceived driving capability, physiological signs and drug concentration measurements. They did not put participants behind the wheel in ordinary traffic, establish a legal impairment cutoff, or validate a sex-specific equation that predicts how a particular driver will behave. The question is narrower than whether an energy drink makes a person “sober,” and narrower than whether men and women are interchangeable in every task.
Who participated, and why does the four-condition design matter?
The definitive experiment enrolled 28 healthy volunteers: 14 men and 14 women, with mean age 22.18 years. The participants were selected social drinkers who had experience with binge drinking and caffeine-containing beverages. Participants were 18–40 years old by eligibility criteria, with other medical and substance-use exclusions; women were assessed during the follicular phase of their menstrual cycle. This is a comparatively narrow laboratory population rather than a representative sample of every age, weight, medical condition or driving history.
Each of the same 28 people attended four experimental sessions in a balanced randomized order, separated by at least three days. The investigators and participants were blinded to assigned beverages, with matched placebos. Therefore, the four conditions represent repeated exposures in a crossover design—not 112 separate individuals. That distinction matters when interpreting precision, independence and denominator claims.
| Condition | What was administered | What the contrast can test |
|---|---|---|
| A | Alcohol with placebo energy drink | Alcohol-related effects without the active energy-drink ingredients |
| A/ED | Alcohol together with active energy drink | Whether adding the drink changes outcomes relative to A |
| ED | Placebo alcohol together with active energy drink | Energy-drink effects without active ethanol |
| P | Both placebo alcohol and placebo energy drink | Control performance and symptoms without either active drink |
Each condition was completed by 14 men and 14 women. One male placebo-condition observation was excluded as an outlier for certain tracking and vigilance analyses. The full statistical design incorporated alcohol, energy drink and enrolled sex/gender as factors, including interactions. A significant change within one sex cannot by itself establish a statistically significant difference between the sexes.
How much alcohol and energy drink did participants receive?
The main study administered 70 grams of ethanol to men and 55 grams to women, from vodka, and paired active-energy-drink conditions with 750 mL for men and 589 mL for women. This drink contained caffeine and taurine; the active energy-drink volume corresponded to approximately 240 mg caffeine in men and about 189 mg in women. Drinks were split into six portions over approximately 80 minutes. The amounts were deliberately different so that the resulting breath ethanol exposures could be compared across groups without simply giving both groups the same absolute grams.
Those gram doses were administered amounts, not measured absorbed quantities. The experimental schedule was intended to resemble a rapid heavy-drinking episode, but its structured serving intervals, control beverages, training and observation differ from the unpredictability of a roadside event. Comparisons also reflect the study’s particular vodka-and-energy-drink formulations; they do not create a universal rule for every beverage recipe, medication or pattern of consumption.
What was actually measured as alcohol concentration?
Researchers measured ethanol in exhaled breath, using an alcohol-testing instrument. In the alcohol-only condition, the reported group mean peak breath alcohol was 0.47 ± 0.07 mg/L for men and 0.46 ± 0.06 mg/L for women; with alcohol plus energy drink, it was 0.46 ± 0.06 mg/L for men and 0.46 ± 0.05 mg/L for women. These are group means and standard deviations in breath units, not individual court-certified whole-blood values. The study found comparable unadjusted peak and time-integrated breath exposures across the enrolled men and women.
A percentage “BAC” appearing in a discussion of breath testing generally presupposes a blood–breath conversion or equivalent display convention. It does not mean the researchers drew a matched venous whole-blood specimen and assayed its ethanol by headspace gas chromatography. Here, the blood samples analyzed by liquid chromatography–tandem mass spectrometry were used for plasma caffeine and taurine, not as independent forensic whole-blood ethanol determinations. Substituting those pharmacokinetic measurements for an ethanol BAC would conflate different analytes and specimen matrices.
For a separate discussion of the distinction between specimen analysis and calculations based on limited blood samples, see the site’s two-blood-sample alcohol-elimination research brief. Neither that topic nor this breath-exposure experiment supplies an individual conversion factor for an unrelated driver.
Did equal-looking breath exposure mean identical biological response?
No. Comparable group mean BrAC curves do not force identical distribution, central nervous system response, body composition, dose-normalized kinetics or self-reported feelings. Indeed, because women received fewer grams, dose-adjusted breath alcohol exposure differed even where the unadjusted group means were similar. That observation concerns exposure per gram administered, not an experimentally measured individual volume of distribution.
The authors also measured caffeine in plasma. When alcohol and the energy drink were combined, group mean peak plasma caffeine was approximately 4,500 ng/mL in men and 4,635 ng/mL in women. Caffeine’s appearance in plasma is a direct analyte measurement, whereas the study’s reported drunkenness, alertness and confidence were subjective rating scales. Neither the presence of plasma caffeine nor a change in confidence provides a direct test of a specific person’s steering, braking or collision avoidance.
What happened on the tracking and vigilance tasks?
Alcohol increased latency in the psychomotor vigilance task and worsened measures of the computer tracking test. Participants attempted to keep two onscreen vehicles centered in corresponding lanes with joysticks. An error was recorded when a displayed vehicle stayed outside its simulated lane for more than 0.4 seconds. This measures visuomotor control in a controlled test, not real steering through moving traffic. A five-minute psychomotor vigilance task separately measured response latency to a predictable-location visual stimulus presented at unpredictable times.
Adding an active energy drink sometimes reduced those measured impairments. For example, in the men, the source’s baseline-referenced peak tracking-error change was 10.64 ± 10.87 in alcohol alone versus 2.36 ± 6.99 with alcohol plus energy drink; the reported within-men A/ED-minus-A effect estimate was −8.29, with a 95% confidence interval of −15.29 to −1.29. In women, corresponding group changes were 4.14 ± 9.17 and 3.71 ± 8.35, while the A/ED-minus-A estimate was −0.43, with a confidence interval spanning zero (−7.43 to 6.57). These are changes from baseline in experimental task outcomes, not counts of actual traffic violations.
For peak mean vigilance-task latency, the source reports a baseline-referenced change in men of 71.34 ± 29.93 ms with alcohol versus 35.78 ± 32.80 ms with A/ED. The within-men A/ED-minus-A effect estimate was −35.57 ms (95% CI −62.84 to −8.30). In women, comparable values were 71.54 ± 28.88 and 50.28 ± 31.42 ms, with effect estimate −21.26 ms (95% CI −48.54 to 6.01). A smaller alcohol-related latency increase is not proof of unimpaired vigilance, and a significant within-men estimate does not automatically establish a sex-by-treatment interaction.
| Observation | Original study result | Defensible interpretation |
|---|---|---|
| Breath alcohol, peak | Men A 0.47 ± 0.07; men A/ED 0.46 ± 0.06; women A 0.46 ± 0.06; women A/ED 0.46 ± 0.05 mg/L | Similar reported group-level exhaled-breath exposure; not directly assayed whole-blood BAC |
| Tracking-test peak error change | Men A 10.64 ± 10.87 vs A/ED 2.36 ± 6.99; women A 4.14 ± 9.17 vs A/ED 3.71 ± 8.35 | Selected task-level improvements with energy drink; not an established men–women interaction or road-driving validation |
| Vigilance peak mean-latency change | Men A 71.34 ± 29.93 vs A/ED 35.78 ± 32.80 ms; women A 71.54 ± 28.88 vs A/ED 50.28 ± 31.42 ms | Alcohol slowed computerized responses; A/ED attenuated some within-condition changes, without removing impairment |
| Self-reported drunkenness | In alcohol-only condition, between-group contrast in eight-hour area-under-effect score 44.82 (95% CI 5.07–84.57), women higher | Difference in a subjective rating summary, not a 44.82-unit BAC or observed road-performance difference |
| Sex comparison for driving-related task scores | No statistically significant between-group difference established for the measured tracking or vigilance outcomes | Failure to demonstrate a group contrast in 28 people is not proof that every possible difference equals zero |
The paper’s numerical tables report some effects as peak baseline-referenced changes and others as time-integrated area-under-effect summaries. Treating those changes as absolute raw performance scores would misread the measurement. Likewise, different confidence intervals describe different comparisons; the main forensic issue is whether the proposed conclusion actually matches the experiment’s tested contrast.
Were there statistically demonstrated differences between men and women?
Not in the principal laboratory driving-related performance comparisons in this sample. The authors did not demonstrate significant sex/gender differences in the observed psychomotor-vigilance latency, tracking time outside the displayed lane, or other driving-related task indices at their matched unadjusted breath exposure. Their results did include trends in some dose-adjusted measures, but a trend is not a confirmed effect and must not be converted into a sex-specific diagnostic threshold.
The distinction between an interaction and two subgroup contrasts is particularly important in expert testimony. Suppose an energy drink changes a test result significantly among men, but not significantly among women. That pattern alone does not prove that its effect is significantly different in men and women. A direct statistical interaction or properly specified between-group contrast is needed. In the source’s tracking and vigilance table, the alcohol-by-energy-drink interaction for those outcomes was reported as not significant. The lack of a demonstrated interaction does not prove pharmacological independence or true equivalence.
Why did subjective drunkenness differ when performance comparisons did not?
Subjective ratings capture an internal experience, while computerized tasks record performance under a standardized challenge. A person can report stronger intoxication without a demonstrably worse score on a particular task, or report feeling capable while performing poorly. This experiment illustrates why self-perception and direct performance should not be substituted for each other.
In the alcohol-only session, women reported significantly higher time-integrated drunkenness, with a study-reported between-group eight-hour effect estimate of 44.82 and 95% confidence interval 5.07 to 84.57. The sedative-type ARCI-PCAG scale likewise showed a higher women’s score: the source’s A-condition area-under-effect estimate was 11.61 (95% CI 1.51–21.81). The paper did not find a corresponding confirmed sex difference across its specific driving-related laboratory outcomes. Both propositions can be true.
The same self-reports are not calibrated measures of blood ethanol, horizontal gaze nystagmus, legally defined impairment, truthfulness, or future willingness to drive. An expert evaluating a witness’s asserted intoxication would need to identify the actual question asked, time of rating, scale, surrounding evidence and whether there were any objective tests of the claimed behavioral effect.
Did caffeine neutralize alcohol or materially lower BrAC?
No demonstrated neutralization follows from the study. Energy drinks improved some measures relative to alcohol alone but did not eliminate alcohol’s observed effects. In fact, participants continued to describe feeling drunk when alcohol and the energy drink were combined. The measured breath-ethanol peaks remained similar between A and A/ED conditions within each sex; the original comparison reported p = 0.994 in men and p = 0.998 in women for breath-ethanol peak concentration. Those large p-values mean a difference was not detected under this design; they do not independently establish chemical identity, absolute equality, or a universal zero interaction.
The study documented higher plasma caffeine concentrations when the energy drink was consumed with alcohol than with the active energy drink alone. That is a different pharmacokinetic issue from whether alcohol was eliminated faster. Caffeine effects on attention cannot be used to revise an ethanol result without actual supporting ethanol measurements, nor can apparent reaction-time improvement be used as a substitute for a legal or clinical impairment assessment.
What does the lack of a significant alcohol–energy drink interaction mean?
The investigators modeled alcohol, active energy drink and sex/gender, including combinations of those predictors. On their measured psychomotor outcomes, they did not identify a general statistically significant alcohol-by-energy-drink interaction. Several within-condition differences existed, however, and interactions for some nonperformance outcomes—such as headache and certain cardiovascular measures—were noted. It would be inaccurate to generalize the psychomotor null to every organ system or to state that the substances never interact.
Interaction tests are also limited by sample size, variability and the prespecified measurement scale. Twenty-eight selected volunteers offer relatively little information about uncommon adverse responses or small between-sex differences. A negative result is best expressed as “not demonstrated in this study,” rather than “scientifically impossible” or “proved identical.” These distinctions matter when a report offers a broad assertion of safety based on one narrowly defined endpoint.
What is the difference between computer tracking and actual driving impairment?
The test used joysticks and two displayed cars. It included errors, time outside a projected lane, and changes in control direction. Those outcomes may respond to alcohol and can help researchers study component visuomotor abilities. But actual driving depends on additional elements: scanning, route selection, distractions, traffic interactions, anticipation, pedal operation, visual conditions and vehicle dynamics. A task’s relation to driving does not make it a validated replacement for on-road performance or a forensic reconstruction of an individual collision.
The study did not observe ordinary road driving, standardized field sobriety tests in arrested drivers, prospective crashes, or real-time eyewitness behavior. It did not generate a sensitivity or specificity for identifying a driver above any statutory blood concentration limit, or a probability that a named person failed to stop. The results can inform questioning about mechanism and methodology, but not establish a case-specific endpoint that was never measured.
How should an expert use the findings in litigation?
First, establish which measured fact is actually at issue: an instrument’s breath reading, a directly analyzed blood sample, a plasma caffeine result, a subjective report of drunkenness, or a scored psychomotor task. Each has a different evidentiary role. The study’s breath values cannot be described as direct venous whole-blood gas-chromatography measurements, and an individual’s BAC should not be reconstructed merely from a published group average.
Second, reproduce the relevant comparison rather than quoting only a favored result. Separate A versus placebo, A/ED versus A, men versus women and interaction tests. State whether a value is raw, change from baseline, dose adjusted or integrated over time, and carry through the denominator and confidence interval. An apparent subgroup improvement does not necessarily establish a general interaction.
Third, tie the inference to the studied population and task. These were mostly young, screened, experienced drinkers who received controlled amounts in a laboratory with training and structured monitoring. The design excludes many real-world factors and is not an identification test for actual impaired driving. A reliable opinion about an incident needs properly obtained case evidence, matrix-specific toxicology, timing, alternative explanations and a scientifically justified bridge between measured function and the alleged event.
For further original study appraisals and the distinction between source material and interpretation, use the forensic toxicology research library. The site’s editorial and research source policy explains its source-evaluation framework.
Frequently asked questions
1. Did women reach a higher breath alcohol concentration than men?
Not in the reported unadjusted group means. Peak breath alcohol clustered around 0.46 mg/L in both groups because different gram doses were administered. Dose-normalized comparisons are different from the comparison of measured group means and do not establish any individual’s venous whole-blood BAC.
2. Does a nonsignificant sex difference prove equal impairment?
No. The experiment did not demonstrate a difference on its selected laboratory outcomes. A study with 14 participants per sex cannot prove exact equivalence across all tasks, doses, ages, diseases, medications and driving contexts.
3. If a tracking score improved after an energy drink, was driving ability restored?
No. A partial improvement in a joystick tracking or visual reaction-time task is not an on-road validation, and alcohol-related deficits remained. The study did not test real vehicle operation or individual collision risk.
4. Was the reported 0.46 mg/L a direct whole-blood test?
No. It is the reported concentration of ethanol in exhaled breath. Plasma concentrations reported elsewhere in the study measured caffeine and taurine, not directly assayed forensic whole-blood ethanol.
5. Why might someone feel more intoxicated without performing worse on a particular task?
Subjective drunkenness and test performance measure different constructs. Their association depends on task demands, timing, expectations and individual variability. A difference in self-reported feeling is not automatically a difference in every objectively observed behavior.
6. Can the published averages calculate a particular driver’s legal BAC or reaction time?
No. Group mean breath readings and laboratory task changes cannot supply an individual’s breath–blood ratio, blood alcohol history, performance score or fault in a specific incident. Case-specific measurements and validated inference methods would be required.
7. Does this study show that alcohol and energy drinks never interact?
No. A generalized psychomotor interaction was not demonstrated, but some within-condition differences and nonperformance interactions were reported. The correct conclusion is limited to the measured outcomes, participants, exposure schedule and statistical power.
Source and bottom line
Primary original research: Hladun O, Papaseit E, Poyatos L, et al. “No significant gender differences in driving-related skills following alcohol mixed with energy drinks during an experimental binge-drinking episode.” Frontiers in Pharmacology. 2025;16:1581229. doi:10.3389/fphar.2025.1581229. The study is a randomized, double-blind four-condition crossover experiment in 28 selected adults, not a field validation of impaired-driving detection.
Bottom line: At similar measured breath ethanol exposures, this trial detected differences in some subjective responses but did not establish significant male–female contrasts in its selected laboratory driving-related skills. Active energy drinks reduced certain test deficits without erasing alcohol’s effects. None of these group results independently proves a named person’s blood concentration, capacity to drive, eyewitness accuracy, or causation of an event.