( ( In addition ) ( , ( ( by ( inhibiting CYP2A6 ) ) ( , ( smoking ( ( can ( be ( decreased ( in ( tobacco-dependent individuals ) ) ) ) ) . ) ) ) ) ) )
(ROOT (S (PP (IN In) (NP (NN addition))) (, ,) (PP (IN by) (S (VP (VBG inhibiting) (NP (NNP CYP2A6))))) (, ,) (NP (NN smoking)) (VP (MD can) (VP (VB be) (VP (VBN decreased) (PP (IN in) (NP (JJ tobacco-dependent) (NNS individuals)))))) (. .)))
In addition, by inhibiting CYP2A6, smoking can be decreased in tobacco-dependent individuals.
(ROOT (S (NP (NP (NN Smoking) (NN tobaccowould)) (ADJP (RBS most) (JJ likely))) (VP (VBP have) (NP (NP (DT a) (JJ negative) (NN impact)) (PP (IN on) (NP (NP (DT the) (NN ability)) (PP (IN of) (NP (DT an) (ADJP (JJ individual) (S (VP (TO to) (VP (VB succeed) (PP (IN at) (NP (JJ physical) (NNS activities))) (SBAR (IN because) (S (NP (PRP it)) (NP (PRP it)))))))) (NNP decreases) (NN stamina) (CC and) (JJ cardiovascular) (NN efficiency))))))) (. .)))
Smoking tobaccowould  most likely have a negative impact on the ability of an individual to succeed at physical activities because it it decreases stamina and cardiovascular efficiency.