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Dtsch Arztebl Int. 2009 May;106(20):341-7. doi: 10.3238/arztebl.2009.0341. Epub 2009 May 15.

Knock-out drugs: their prevalence, modes of action, and means of detection.

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Institut für Rechtsmedizin der Universität Bonn, Bonn, Germany.



Knock-out drugs are used to facilitate the commission of a crime, generally either robbery or sexual assault. Although media reports on the use of knock-out drugs have become more frequent, there are no robust epidemiological data on the incidence of drug-facilitated robbery or sexual assault, presumably because many crimes of these types do not enter into official statistics.


The authors describe the modes of action and toxicological means of detection of the substances most frequently used as knock-out drugs on the basis of a selective literature research on the terms "drug-facilitated sexual assaults" (DFSA) and "drug-facilitated crimes" (DFC).


The most frequently used drug in cases of sexual assault is still alcohol (ca. 40% to 60%), followed by illegal drugs (cannabis, cocaine). The presence of involuntarily consumed medications and drugs of abuse is demonstrated by routine toxicological analysis only in relatively few cases (ca. 2%). The substances most commonly found are benzodiazepines, followed by other hypnotics. In Europe, the illegal substance gamma-hydroxybutyric acid (GHB, "Liquid Ecstasy"), often mentioned as a "date-rape drug," is only rarely detected with sufficient medicolegal certainty. This may be due to its rapid elimination (it is detectable in blood for up to 8 hours, in urine for up to 12 hours) as well as its physiological occurrence in the body. If the toxicological analysis of blood and urine is negative in a case of suspected DFSA, then the analysis of a hair sample about four weeks after the assault can detect the presence of drugs consumed at that time. If the victim has long hair, it may be possible to detect knock-out drugs taken more than four weeks earlier. In Europe, convictions for drug-facilitated crimes are comparatively rare, mainly because of the difficulty of demonstrating conclusive evidence.


A careful medical history and physical examination and the careful taking of biological samples for toxicological analysis form the basis for the detection of drug-facilitated crimes.


benzodiazepine; drug screening; gamma-aminobutyric acid abuse; hair analysis; sex crimes

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