The Collaborative International Dictionary of English v.0.48:

Stimulative \Stim"u*la*tive\, a.
   Having the quality of stimulating. -- n. That which
   stimulates.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stimulative
    adj 1: capable of arousing or accelerating physiological or
           psychological activity or response by a chemical agent
           [ant: depressant]