Possibly, but strychnine is a fairly rapid drug in its action. 
( Possibly ( , ( ( but strychnine ) ( ( is ( ( a ( ( fairly rapid ) drug ) ) ( in ( its action ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB Possibly)) (, ,) (NP (IN but) (NN strychnine)) (VP (VBZ is) (NP (NP (DT a) (ADJP (RB fairly) (JJ rapid)) (NN drug)) (PP (IN in) (NP (PRP$ its) (NN action))))) (. .)))
Strychnine is used to treat flu symptoms in horses. 
( Strychnine ( ( is ( used ( to ( ( treat ( flu symptoms ) ) ( in horses ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Strychnine)) (VP (VBZ is) (VP (VBN used) (S (VP (TO to) (VP (VB treat) (NP (NN flu) (NNS symptoms)) (PP (IN in) (NP (NNS horses)))))))) (. .)))