( ( The molecule ) ( ( competes ( against ( ( the ( ( naturally occurring ) ( chemical dopamine ) ) ) ( for ( ( receptor sites ) ( in ( the brain ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN molecule)) (VP (VBZ competes) (PP (IN against) (NP (NP (DT the) (ADJP (RB naturally) (VBG occurring)) (NN chemical) (NN dopamine)) (PP (IN for) (NP (NP (NN receptor) (NNS sites)) (PP (IN in) (NP (DT the) (NN brain)))))))) (. .)))
The molecule competes against the naturally occurring chemical dopamine for receptor sites in the brain.
(ROOT (S (NP (NNP Addiction)) (VP (VBZ affects) (NP (NP (DT the) (JJ dopamine) (NNS receptors)) (PP (IN within) (NP (DT the) (NN brain))))) (. .)))