Method of providing aripiprazole to patients having impaired cyp2d6 or cyp3a4 enzyme function

A method of initiating aripiprazole treatment in a patient with impaired CYP2D6 or CYP3A4 enzyme function, comprising:

• administering intramuscularly to said patient a starting dose of a long-acting drug-containing suspension which provides therapeutic plasma levels of aripiprazole over a period of about one month;
• wherein said starting dose provides no more than about 75% of the amount of aripiprazole compared to an initial dose recommended for a patient with normal CYP2D6 and CYP3A4 enzyme function.