“…These studies vary in terms of subject selection, types of specific drug items, cut-off values for positive drug-test results, extraneous variables included and methods of exposure measurements (Carmen del Carmen del Rio et al, 2002;Drummer et al, 2004;Engeland et al, 2007;Ferguson et al, 1996;Harrison and Fillmore, 2005;Kasantikul et al, 2005;Laumon et al, 2005;Movig et al, 2004;Ray et al, 1992;Verster and Volkerts, 2004). Most studies included amphetamines, cocaine, cannabis, benzodiazepines and opiates in the reports (Carmen del Carmen del Rio et al, 2002;Drummer et al, 2004;Engeland et al, 2007;Harrison and Fillmore, 2005;Kasantikul et al, 2005;Laumon et al, 2005;Movig et al, 2004;Ray et al, 1992;Verster and Volkerts, 2004). Few studies attempted to address the effect of antihistamines but the results were controversial (http://www/immortal.or.at/).…”