Sentence:  It has further been shown that : ( 1 ) an experimental neurosis in its initial stages is associated with a reversible shift in the central autonomic balance ; ( 2 ) <WSD>drugs</WSD> altering the hypothalamic balance alter conditioned reactions ; ( 3 ) in a state of depression , the positive conditioned stimulus may fail to elicit a conditioned reaction but cause an increased synchrony instead of the excitatory desynchronizing ( alerting ) effect on the EEG . 
Meaning of the word marked with <WSD> tags:  a substance that is used as a medicine or narcotic