Tilapia (Mozambique) fish, belonging to the family Cichlidae and order Cichliformes, are native to freshwater in Africa. Olanzapine, a second-generation antipsychotic drug (APD), is known for its improved efficacy and reduced side effects compared to first generation APDs and is commonly used for treating psychiatric disorders and brain cancer. This study aimed to assess the effects of Olanzapine on the growth, behavior, haematology, and histopathology of Tilapia fish. The fishes were collected from the selected fish farm in Pattoki. The fish were acclimatized for one week and then treated with 0.06 mg/l of Olanzapine daily for 28 days. They were divided into control, treated, and untreated groups. Morphometric measurements, haematological analyses, and histological evaluations of kidney, liver, and gill tissues were conducted. The results indicated significant changes in morphometric characteristics and an increase in movement in treated fish compared to controls. MCH and MCHC levels were significantly higher in the treated group (P<0.005), while other haematological parameters, including WBCs, RBCs, HGB, HCT, MPV, PDW, PCT, and MCV, showed no significant changes (P>0.05). Histopathological analysis revealed notable changes in the kidneys, liver, and gills of Olanzapine-treated fish. Despite non-significant increases in total body weight, Olanzapine positively affected morphometric traits and feeding behavior while causing observable haematological and histological alterations in Tilapia Mozambique. To conclude, the Olanzapine is relatively safe for Tilapia's liver but may harm the gills and kidneys. It had minimal effects on behavior, morphology, and hematology, with significant damage only to gill structure and mild changes in the kidneys.