The Collaborative International Dictionary of English v.0.48:

Loco \Lo"co\, v. t. [imp. & p. p. Locoed; p. pr. & vb. n.
   Locoing.]
   To poison with loco; to affect with the loco disease; hence
   (Colloq.), to render insane or mad. "The locoed novelist."
   --W. D. Howells.
   [Webster 1913 Suppl.]