Synonyms for Insane:

adj.

chaotic (adjective)
amorphous, anarchical, anarchistic, blurry, chaotic, cluttered, confused, deformed, deranged, disarrayed, discomposed, disconnected, disheveled, disordered, disorderly, disorganized, embroiled, formless, frantic, frenzied, fuzzy, inchoate, incoherent, inconsistent, indefinite, indistinct, inexact, irregular, jumbled, lawless, lax, loose, messy, muddled, obscure, perturbed, rambunctious, shapeless, tempestuous, tumultuous, undisciplined, uneven, unruly, wild, Disintegrated, out of control.
crazed (adjective)
berserk.
deranged (adjective)
nutty.
foolish (adjective)
zany, imbecilic, loopy, tomfool, dippy.
haywire (adjective)
haywire, amok.
insane (adjective)
babbling, batty, berserk, blithering, crazy, delirious, demented, feverish, hysterical, irrational, kooky, lunatic, mad, maniacal, neurotic, nutty, psycho, psychotic, schizoid, unbalanced, Crack-brained, brain-sick, deranged, frenzied.
lunatic (adjective)
schizoid.
mentally ill; foolish (adjective)
batty, cracked, crazed, crazy, cuckoo, daft, demented, deranged, frenzied, idiotic, irrational, loony, lunatic, mad, maniacal, moonstruck, nuts, nutty, of unsound mind, paranoid, preposterous, psychopathic, psychotic, rabid, raging, raving, schizophrenic, screwy, touched, unhinged, unsettled, wild.
softheaded (adjective)
softheaded.
touched (adjective)
pixilated.

n.

childish, laughable, ludicrous, over-the-top, ridiculous, not in your right mind/not right in the head. madcap. cuckoo, distraught, gaga, off, sane, wrong, Daffy, bananas. ability, absurd, cockeyed, dopey, imbecilic, jerky, knowledge, moronic, nonsensical, preposterous, sappy, silly, softheaded, tomfool, unearthly, zany, dippy. deranged (noun)
balmy, bats, batty, bonkers, cracked, crazed, crazy, cuckoo, demented, loco, loony, lunatic, mad, nuts, nutty, psychotic, round the bend, screwy, touched, unbalanced, unhinged, bananas.
insane (noun)
amok, amuck, around the bend, balmy, barmy, bats, batty, berserk, bonkers, brainsick, buggy, certifiable, certified, crackbrained, cracked, crackers, crazed, crazy, daft, demented, demoniac, demoniacal, deranged, distracted, disturbed, dotty, fey, foolish, fruity, half-crazed, harebrained, haywire, hebephrenic, idiotic, kookie, kooky, loco, loony, loopy, lunatic, mad, maniac, maniacal, manic-depressive, maniclike, mentally ill, moonstruck, non compos mentis, noncompos mentis, nuts, nutty, of unsound mind, paranoid, possessed, psychopathic, psychopathologic, psychopathological, psychotic, raving, raving mad, round the bend, schizophrenic, screw-loose, screwy, sick, touched, unbalanced, unhinged, unsound, unstable, wacky, whacky, wild.
mentally ill (noun)
bipolar, depressed, diminished responsibility.

v.

deranged (verb)
addlepated, cuckoo, gone, obsessed, pixilated, rabid, raging, rational, sane, unsettled, violent, Deluded, bananas, addleheaded.

Other synonyms:

jerky, laughable, ludicrous, madcap, over-the-top, ridiculous, softheaded, Daffy, bananas, dippy. absurd, cockeyed, distraught, gaga, imbecilic, moronic, nonsensical, preposterous. childish, dopey, sappy, silly, zany. unearthly. wrong. crazy
off.
mentally ill
bipolar, depressed, mentally ill, diminished responsibility.
Other relevant words:
absurd, amok, amuck, around the bend, balmy, barmy, bats, bipolar, bonkers, brainsick, buggy, certifiable, certified, childish, cockeyed, crackbrained, cracked, crackers, crazed, cuckoo, daft, demoniac, demoniacal, depressed, distracted, distraught, disturbed, dopey, dotty, fey, foolish, fruity, gaga, half-crazed, harebrained, haywire, hebephrenic, idiotic, imbecilic, jerky, kookie, laughable, loco, loony, loopy, ludicrous, madcap, maniac, manic-depressive, maniclike, mentally ill, moonstruck, moronic, non compos mentis, nonsensical, nuts, of unsound mind, off, over-the-top, paranoid, possessed, preposterous, psychopathic, psychopathologic, psychopathological, rabid, raging, raving, raving mad, ridiculous, round the bend, sappy, schizophrenic, screw-loose, screwy, sick, silly, softheaded, tomfool, touched, unearthly, unhinged, unsettled, unsound, unstable, violent, wacky, whacky, wrong, zany, Deluded, Daffy, bananas, dippy.

Usage examples for insane

  1. I had no doubt that she was insane – Marital Power Exemplified in Mrs. Packard's Trial, and Self-Defence from the Charge of Insanity by Elizabeth Parsons Ware Packard
  2. The fellow belongs in an insane asylum. – The Future Belongs to the People by Karl Liebknecht
  3. While Alexander of Parma, sorely against his will and in obedience to what, he deemed the insane suggestions of his master, was turning his back on the Netherlands in order to relieve Paris, now hard pressed by the Bearnese, an opportunity offered itself of making at least a beginning in the great enterprise of recovering these most valuable possessions. – Project Gutenberg History of The Netherlands, 1555-1623, Complete by John Lothrop Motley