Several studies reported that it causes alterations in mood, thinking and feelings as seen with other central nervous system stimulants, although modafinil has gained popularity among clinicians due to its low abuse potential. There is a case related to abuse of modafinil in supratherapeutic doses. The data with regard to its use in toxic doses are also limited. Modafinil toxicity levels vary widely among species. In clinical trials on humans, taking up to 1200 mg/day for 7 to 21 days or one-time doses up to 4500 mg did not appear to cause life-threatening effects, although a number of adverse experiences like agitation, insomnia, anxiety, irritability, tremor and cardiovascular changes were observed. In addition to this, there have been concerns about possible psychosis inducing properties of supratherapeutic doses of modafinil. Modafinil induced psychosis may be related to its indirect dopaminergic action through inhibition of GABA secretion and direct dopaminergic action through inhibition of dopamine reuptake. It is plausible that modafinil could exacerbate psychosis. A case report about a 61-year-old patient on clozapine treatment suggested worsening of psychotic symptoms due to modafinil use and improving of those symptoms with cessation of modafinil. Also in a study which was investigating modafinil effects on schizophrenic patients, while most patients appear to tolerate the drug well, several cases have been reported where patients, who received modafinil suffered from psychotic relapse or worsening of already existing psychotic symptoms. In this case presentation, we intend to emphasize that modafinil might have an aggravating effect on psychotic symptoms and attention must be paid to modafinil abuse in clinical practice. A 29-year-old male patient, started to use modafinil 9 months ago because of hypersomnia and continued to use it at a dose of 200 mg/d for 5 months. After 5 months, since he was feeling angry, slumbery and he had difficulty to concentrate, the patient increased his daily modafinil use up to 2000-3000 mg/d without consulting any physician. When patient applied to our clinic, he hadn’t been using modafinil for 4 days; delusions of reference and jealousy were noticed in his examination. Psychotic symptoms of the patient, who was treated with olanzapine 20 mg/d for 28 days of hospitalization, subsided in a few weeks. In his outpatient follow-up, he continued to get 10mg/d of olanzapin treatment. In further follow up, patient stated that he used 800 milligrams of modafinil 20 days ago, and aggravation of his psychotic symptoms were observed while he was treated with olanzapine 10 mg/d. He is still in our clinic’s follow-up programme with the diagnosis of psychotic disorder. It is known that substance and drug abuse is higher in individuals with psychotic disorder than the general population. In our case, in addition to abuse of modafinil; it was seen that there were increase in psychotic symptoms due to abuse of modafinil even while using antipsychotic medication. Clinicians should bear in mind that there may be abuse of modafinil in patients with psychotic disorder and this abuse may cause worsening of psychotic symptoms.