The Collaborative International Dictionary of English v.0.48:

Dopey \Dop"ey\, Dopy \Dop"y\, a.
   1. stupid; as, a dopy kid. [Colloq.]

   Syn: cloddish, doltish.
        [PJC]

   2. [affected by dope[2].] dulled or stupefied by alcohol or
      narcotics; sluggish or dull as though under the influence
      of a narcotic. [Slang]
      [Webster 1913 Suppl. + WordNet 1.5 +PJC]

   3. revealing stupidity; as, a dopey answer. [WordNet sense 2]

   Syn: anserine, dopey, fool(prenominal), foolish, goosey,
        goosy, gooselike.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dopey
    adj 1: having or revealing stupidity; "ridiculous anserine
           behavior"; "a dopey answer"; "a dopey kid"; "some fool
           idea about rewriting authors' books" [syn: anserine,
           dopy, dopey, foolish, goosey, goosy,
           gooselike, jerky]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "dopey":
   abeyant, apathetic, bedazzled, benumbed, blase, blunt,
   blunt-witted, bored, cataleptic, catatonic, comatose, dazed,
   dazzled, dead, debilitated, dim, dim-witted, dormant, droopy,
   drugged, dull, dull of mind, dull-headed, dull-pated, dull-witted,
   enervated, exanimate, fat-witted, flat, foul, groggy, gross-headed,
   heavy, hebetudinous, in a daze, in abeyance, in suspense, inactive,
   inanimate, inert, jaded, knocked silly, lackadaisical, languid,
   languorous, latent, leaden, lethargic, lifeless, listless, logy,
   lumpish, mazed, moribund, numb, obtuse, passive, phlegmatic,
   pooped, punch-drunk, punchy, sated, sedentary, silly, slack,
   slaphappy, sleeping, sleepy, slow, slow-witted, sluggish,
   slumbering, slumberous, smoldering, somnolent, stagnant,
   stagnating, standing, static, stultified, stupid, supine,
   suspended, tame, thick-brained, thick-headed, thick-pated,
   thick-witted, thickskulled, torpid, unaroused, vegetable,
   vegetative, wan, weary, wooden, woozy, world-weary