The Collaborative International Dictionary of English v.0.48:

Moonstruck \Moon"struck`\ (m[=oo]n"str[u^]k`), a.
   1. Mentally affected or deranged by the supposed influence of
      the moon; lunatic.
      [1913 Webster]

   2. Produced by the supposed influence of the moon.
      "Moonstruck madness." --Milton.
      [1913 Webster]

   3. Made sick by the supposed influence of the moon, as a
      human being; made unsuitable for food, as fishes, by such
      supposed influence.
      [1913 Webster]

WordNet (r) 3.0 (2006):

moonstruck
    adj 1: insane and believed to be affected by the phases of the
           moon [syn: lunatic, moonstruck]