Use of antianxiety drugs as countermeasures in the detection of guilty knowledge

This 1992 study by Iacono and colleagues evaluated whether three common antianxiety drugs—diazepam, meprobamate, and propranolol—could enable guilty subjects to evade detection on the Guilty Knowledge Test. Seventy-five undergraduates were divided into innocent and guilty groups, with guilty participants receiving one of the three drugs or placebo before testing. The results demonstrated that none of the medications affected GKT outcomes, providing strong evidence for the test's resistance to pharmaceutical countermeasures.

Laboratory study with 75 undergraduate participants divided into one innocent and four guilty groups (three drug conditions plus placebo). Participants viewed videotaped mock crime scenarios and underwent GKT testing after drug administration, with recognition memory assessments conducted post-test.

This laboratory study investigated whether commonly prescribed antianxiety medications could enable guilty individuals to evade detection on the Guilty Knowledge Test. Using a mock crime paradigm, 75 participants were divided into innocent and guilty groups, with guilty participants receiving either diazepam, meprobamate, propranolol, or placebo before polygraph testing. Results demonstrated that none of the pharmaceutical agents compromised the GKT's detection capability, with guilty participants identified at similar rates across all conditions. An incidental finding suggested that innocent participants with higher recognition memory scores for crime details showed elevated guilt scores on the GKT, indicating a potential source of false positives.

The findings provide reassurance that the GKT maintains its validity even when subjects use commonly available antianxiety medications, supporting its robustness against pharmaceutical countermeasures in forensic applications.

Background & Context

The vulnerability of polygraph testing to pharmaceutical countermeasures has long been a critical concern in forensic psychophysiology. In the early 1990s, following Iacono's earlier 1984 study on diazepam and methylphenidate, questions remained about whether commonly available antianxiety medications could enable guilty individuals to evade detection on the Guilty Knowledge Test (GKT), now known as the Concealed Information Test (CIT).

This research emerged during a pivotal period when the polygraph field was experiencing increased scrutiny regarding countermeasures. The study tested three different pharmacological agents—diazepam (Valium), meprobamate (Miltown), and propranolol (Inderal)—representing distinct classes of antianxiety drugs with different mechanisms of action. Understanding whether these widely prescribed medications could compromise test validity was essential for both criminal justice applications and the theoretical foundation of the GKT.

Unlike the Comparison Question Test (CQT), which relies on arousal differences between lie and truth-telling, the GKT is grounded in recognition memory and orienting response theory. The critical question was whether dampening physiological arousal through medication could mask the recognition response that guilty individuals display when encountering crime-related details.

Research Design & Methodology

The study employed 75 undergraduate students evenly divided among one innocent group and four guilty groups. This balanced design allowed for both between-group comparisons of drug effects and assessment of false positive rates among innocent participants.

Participants in the guilty groups viewed a videotape depicting a burglary from the perspective of the burglar, designed to encode crime-relevant details into their memory. Each guilty group then received either diazepam, meprobamate, propranolol, or a placebo prior to polygraph testing. The innocent group viewed a neutral videotape showing apartment interiors without any criminal activity.

Key methodological elements included:

• Mock crime paradigm: First-person perspective videotape to create realistic guilty knowledge
• Drug administration: Three pharmacologically distinct antianxiety agents plus placebo control
• GKT protocol: Multiple-choice questioning format focusing on specific details from the staged crime
• Recognition memory assessment: Post-test evaluation to measure participants' actual recall of crime details

Results & Key Findings

The central finding was unequivocal: drug status had no influence on the outcome of the GKT. None of the three antianxiety medications—diazepam, meprobamate, or propranolol—proved effective as countermeasures against the Guilty Knowledge Test. Guilty participants taking drugs were detected at rates comparable to those receiving placebo, demonstrating the GKT's robustness against this category of pharmaceutical intervention.

An unexpected finding emerged regarding innocent participants: innocent subjects who coincidentally obtained high scores on a recognition memory test covering details of the mock crime tended to obtain higher guilt scores on the GKT. This suggests that false positives may correlate with incidental knowledge about crime details, even when that knowledge was acquired innocently.

The results can be summarized as follows:

• Diazepam (benzodiazepine): No countermeasure effect observed
• Meprobamate (carbamate): No countermeasure effect observed
• Propranolol (beta-blocker): No countermeasure effect observed
• Detection remained effective across all drug conditions for guilty participants
• Memory encoding proved more important than arousal modulation for GKT validity

Discussion & Significance

The findings provide strong evidence that the GKT's theoretical foundation—recognition memory and orienting responses—is more resilient to pharmacological manipulation than autonomic arousal alone. As later reviews noted, diazepam, meprobamate, and propranolol were all found to be ineffective as countermeasures to the CIT, establishing this study as a landmark demonstration of the test's resistance to common anxiolytic drugs.

This research contrasts importantly with findings on mental and physical countermeasures, which have shown some effectiveness against the GKT. The distinction suggests that while conscious cognitive strategies can disrupt detection, passive pharmacological dampening of arousal cannot overcome the fundamental memory-recognition process underlying guilty knowledge detection. The GKT appears to tap into cognitive processes that remain intact even when peripheral physiological responses are pharmacologically attenuated.

The incidental finding about innocent participants with coincidental knowledge has significant theoretical implications. It highlights that the GKT's specificity depends critically on controlling information leakage—innocent suspects who happen to know crime details through media exposure or other sources may show false positive responses. This underscores the importance of withholding critical crime information from public disclosure when GKT/CIT testing is contemplated.

Limitations & Considerations

The study employed a laboratory analog design using undergraduate students and a simulated crime scenario, which may not fully capture the psychological state of actual criminal suspects facing real consequences. Drug dosages were necessarily limited by ethical considerations and may not reflect the higher doses that motivated guilty individuals might self-administer in actual forensic contexts.

The mock crime involved passive viewing of a videotape rather than active participation in a criminal act, potentially affecting both the strength of memory encoding and the emotional salience of the "guilty knowledge." Additionally, the study examined only single-dose acute effects; chronic use or higher doses of these medications might theoretically produce different outcomes, though ethical constraints prevented testing such scenarios.

Practical Applications

For polygraph examiners and law enforcement, this research provides reassuring evidence that common prescription anxiolytics are unlikely to compromise GKT/CIT validity. Examiners need not routinely screen for or exclude examinees using these medications, though documentation of drug use remains advisable. The finding that recognition memory rather than anxiety level drives GKT outcomes reinforces the test's conceptual superiority over arousal-based methods when properly applied.

The study's implications extend to courtroom arguments about GKT admissibility. Defense claims that antianxiety medication could produce false negatives lack empirical support based on this research. However, the findings regarding incidental knowledge among innocent participants underscore the critical importance of information control in criminal investigations—prosecutors and investigators must rigorously protect crime scene details to preserve the GKT's discriminative power and prevent false accusations based on inadvertently acquired knowledge.