functional hallucinations are an unusual form of perceptual disorder , in which hallucinations are triggered by a stimulus in the same modality , and co - occur with it . for example , a patient may report hearing voices criticizing him every time he hears the sound of a rotating fan , and which stop when the fan is not running . their exact significance is unknown , but they have been reported in schizophrenia and other functional psychotic disorders . the treatment of positive symptoms of schizophrenia , including hallucinations , generally involves the use of antipsychotics . the following is the report of a patient diagnosed with schizophrenia , with persistent functional hallucinosis , who responded to the addition of sodium valproate . a single man , aged 30 , employed in a factory , presented to our outpatient department , in 2007 , with two years continuous illness , characterized by persistent auditory hallucinations , secondary delusions of reference , social withdrawal , and impaired occupational functioning . he also reported obsessive doubts about routine activities , such as closing doors or taps , and a compulsion to check whether he had done these properly , despite knowing that this was unnecessary . he was diagnosed to have paranoid schizophrenia and obsessive - compulsive disorder , and was treated with risperidone ( titrated up to 8 mg / day ) and fluoxetine ( titrated up to 80 mg / day ) . on the above - mentioned medications , he improved significantly , and was able to return to his job . his job involved frequent contact with machinery and motors . whenever he heard these machines running he found these distressing , and this led him to frequently avoid his work or leave it incomplete . he did not hear these voices at any other time , and did not report any recurrence of his other symptoms . his body weight was 62 kg . due to financial difficulties ( the patient was receiving the above medications free of cost from the hospital ) and his overall good response to risperidone therefore , he was given a trial of adjunctive sodium valproate , which was freely available in the hospital and had some evidence of efficacy in reducing positive symptoms , as an adjunct to antipsychotics . after obtaining the patient 's consent , sodium valproate was initiated at a dose of 600 mg / day , and gradually increased by 200 mg every week based on his response and adverse effects . at 1000 mg / day of sodium valproate , the patient reported a significant reduction in his hallucinations , and he felt that he could carry out most of his work . hence , valproate was further increased at the same rate , up to 1800 mg / day . at this dose , the patient reported feeling  near - normal , and was in line for a promotion at his workplace . however , he developed significant postural tremors , which interfered with his ability to work , and valproate was reduced to 1700 mg / day . at this dose , he reported that the voices  had decreased by 75% , and he scored between 2 and 3 ( mild symptoms ) on item p3 ( hallucinations ) of the positive and negative symptom scale for schizophrenia . he has remained on valproate 1700 mg / day , along with risperidone 8 mg / day and fluoxetine 80 mg / day , for the past three months , and has remained stable . his functional hallucinations still occur from time to time at work , but he is less bothered by them and does not experience any impairment . the management of patients with schizophrenia , who have a single persistent symptom , is a challenging situation . evidence - based treatments , such as changes in medication or cognitive - behavioral therapy , may not always be feasible . in this patient , time and economic constraints made it unlikely that the patient would comply with either . hence , an alternative that would be safe , affordable , and with some evidence of effectiveness was required . on account of the rarity of functional hallucinations however , a single case report suggests that carbamazepine may be helpful . in psychiatry , a cochrane review suggests that it may be useful in reducing aggression and tardive dyskinesia , but has little effect on other symptoms . however , one trial has suggested that adjunctive divalproex reduces positive symptoms , and a case series found the addition of valproic acid useful in  difficult - to - treat schizophrenia patients . the effect of adjunctive valproate in schizophrenia is probably not due to the elevation of risperidone levels . valproate acts primarily through gamma - amino butyric acid ( gaba)-ergic mechanisms , which may modulate the actions of dopamine . alternately , it may act through an epigenetic mechanism involving the demethylation of relevant sections of the gaba - related genes . finally , given the paroxysmal , event - triggered nature of the patient 's hallucinations , it is possible that valproate 's ability to block sodium channels in a use - dependent fashion , may have contributed to symptom amelioration , as carbamazepine did in the earlier case . although it can not be recommended in all patients , this case suggests that valproate may be beneficial in selected cases , particularly as an add - on to antipsychotics .