atypical

:  not usual or normal:  not typical an atypical case

1:  not typical :  not like the usual or normal type The procedure, ductal lavage, washes cells from the milk ducts, where 95 percent of breast cancers start. Tests can then be performed to look for atypical or abnormal cells.—Judith Groch, The New York Times, 20 Nov. 2001 The results of treatment of patients with gallstones are less successful in individuals with atypical pain patterns or painless dyspepsia …—The Journal of the American Medical Association, 24 Feb. 1993 In some patients with atypical dysgenesis, the smear may show slight proliferation.—George L Wied et al., Compendium on Diagnostic Cytology, 1976

2:  relating to or being an antipsychotic drug (such as aripiprazole and risperidone) that tends to produce fewer adverse side effects on movement (such as akathisia or dyskinesia) than previously used antipsychotic drugs (such as haloperidol) Atypical antipsychotics work more precisely, manipulating both dopamine and serotonin and suppressing symptoms without causing so many associated problems.—Jeffrey Kluger, Time, 19 Aug. 2002 Although studies indicated that the atypical drugs are similar to the conventional drugs in reducing psychotic symptoms and produce few neurologic effects, the evidence of their superior efficacy has been neither consistent nor robust …—Jeffrey A. Lieberman et al., The New England Journal of Medicine, 22 Sept. 2005

:  an atypical antipsychotic drug (see atypical[1] 2) Her 24-year-old daughter, diagnosed with schizophrenia in 1993, had problems with two types of atypicals before a third proved successful.—Stephaan Harris, USA Today, 28 June 1999