( ( While ( ( ( a number ) ( of drugs ) ) ( have ( been ( employed ( in ( chemical ( aversion therapy ) ) ) ) ) ) ) ) ( , ( ( ( the three ) ( most ( commonly used ) ) ) ( ( are ( emetine ( , ( apomorphine ( , ( and lithium ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN While) (S (NP (NP (DT a) (NN number)) (PP (IN of) (NP (NNS drugs)))) (VP (VBP have) (VP (VBN been) (VP (VBN employed) (PP (IN in) (NP (JJ chemical) (NN aversion) (NN therapy)))))))) (, ,) (NP (NP (DT the) (CD three)) (ADJP (RBS most) (RB commonly) (VBN used))) (VP (VBP are) (NP (NN emetine) (, ,) (NN apomorphine) (, ,) (CC and) (NN lithium))) (. .)))
While a number of drugs have been employed in chemical aversion therapy, the three most commonly used are emetine, apomorphine, and lithium.
(ROOT (S (NP (NNP Lithium)) (VP (VBZ has) (NP (CD three) (NNS electrons))) (. .)))