( ( In ( Table 1 ) ) ( , ( ( ( ( the ( psychoactive drugs ) ) ( ( most widely ) ( used ( by humans ) ) ) ) ( -- ( ( ( caffeine , ) ( alcohol ( , ( nicotine ( , ( marijuana ( , ( and benzodiazepines ) ) ) ) ) ) ) ) -- ) ) ) ( ( are ( those ( ( that animals ) ( are ( least ( likely ( to ( self-administer ( in ( the laboratory ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NNP Table) (CD 1))) (, ,) (NP (NP (DT the) (JJ psychoactive) (NNS drugs)) (VP (ADVP (RBS most) (RB widely)) (VBN used) (PP (IN by) (NP (NNS humans)))) (PRN (: --) (NP (NP (NN caffeine)) (, ,) (NP (NN alcohol) (, ,) (NN nicotine) (, ,) (NN marijuana) (, ,) (CC and) (NN benzodiazepines))) (: --))) (VP (VBP are) (NP (NP (DT those)) (SBAR (WHNP (WDT that) (NNS animals)) (S (VP (VBP are) (ADJP (RBS least) (JJ likely) (S (VP (TO to) (VP (VB self-administer) (PP (IN in) (NP (DT the) (NN laboratory)))))))))))) (. .)))
In Table 1, the psychoactive drugs most widely used by humans -- caffeine, alcohol, nicotine, marijuana, and benzodiazepines -- are those that animals are least likely to self-administer in the laboratory.
(ROOT (S (NP (NN Caffeine) (CC and) (NN alcohol)) (VP (VBP are) (NP (NP (CD two) (NNS examples)) (PP (IN of) (NP (DT a) (NN psychoactive))))) (. .)))
Caffeine and alcohol are two examples of a psychoactive.