The smallest amount that will produce the desired results must be carefully determined for each individual, since optimal dosage levels of this potent drug vary from patient to patient. In general, the oral dose has been found to be approximately two to three times the parenteral dose of fluphenazine. Treatment is best instituted with a low initial dosage , which may be increased, if necessary, until the desired clinical effects are achieved. Therapeutic effect is often achieved with doses under 20 mg daily. Patients remaining severely disturbed or inadequately controlled may require upward titration of dosage. Daily doses up to 40 mg may be necessary; controlled clinical studies have not been performed to demonstrate safety of prolonged administration of such doses.