At the request of the U.S. Food and Drug Administration, the pharmaceutical company Pfizer has issued an important drug warning letter announcing the addition of new information to the CONTRAINDICATIONS and PRECAUTIONS sections of the Zoloft label, contraindicating the concomitant use of pimozide (a tranquilizer) with the antidepressant.

Since the highest recommended pimozide dose (10 mg) has not been evaluated in combination with Zoloft, its effect on QT interval and PK parameters at doses higher than 2 mg at this time is not known. While the mechanism of this interaction is unknown, due to the narrow therapeutic index of pimozide, concomitant administration of Zoloft and pimozide is now contraindicated.