[2] It is used in the treatment of chronic psychoses such as schizophrenia,[2][3] and appears to be about equal in effectiveness to low-potency antipsychotics like chlorpromazine.

[5] Common side effects include movement problems, sleepiness, depression and increased weight.

[2] Serious side effects may include neuroleptic malignant syndrome, low white blood cell levels, and the potentially permanent movement disorder tardive dyskinesia.

[2] It may also increase prolactin levels which may result in milk production, enlarged breasts in males, impotence, and the absence of menstrual periods.

[10] Another 2018 Cochrane review found that there was limited evidence that newer atypical antipsychotics were more tolerable than fluphenazine.

[14] Fluphenazine acts primarily by blocking post-synaptic dopaminergic D2 receptors in the basal ganglia, cortical and limbic system.

[9] In horses, it is sometimes given by injection as an anxiety-relieving medication, though there are many negative common side effects and it is forbidden by many equestrian competition organizations.