ADDITIVE DEPRESSANT EFFECT WITH SEDATIVES, HYPNOTICS, ANTIHISTAMINES, OPIATES AND ALCOHOL. WHEN USED CONCOMITANTLY, ABOUT 1/4 TO 1/2 THE USUAL DOSAGE OF SUCH AGENTS IS REQUIRED. POTENTIATION OF ANTICHOLINERGIC EFFECTS OF ANTIPARKINSON AGENTS. ADDITIVE ORTHOSTATIC HYPOTENSIVE EFFECT WITH MAOI. REVERSES ANTIHYPERTENSIVE EFFECT OF GAUENTHIDINE, METHYLDOA AND CLONIDINE. INCREASED RISK OF ARRHYTHMIAS WITH ANTIMALARIALS, TRICYCLIC ANTIDEPRESSANTS, ANTIHISTIMINES AND CISAPRIDE. NEUROLEPTIC DRUGS ELEVATE PROLACTIN LEVELS. CHLORPROMAZINE DIMINISHES THE EFFECT OF ORAL ANTICOAGULANTS. PHENOTHIAZINES CAN PRODUCE ALPHA-ADRENERGIC BLOCKADE.
CHLORPROMAZINE MAY LOWER THE CONVULSIVE THRESHOLD; DOSAGE ADJUSTMENTS OF
ANTICONVULSANTS MAY BE NECESSARY. CHLORPROMAZINE MAY INTERFERE WITH
THE METABOLISM OF DILANTIN AND THUS PRECIPITATE DILANTIN TOXICITY. CONCOMITANT ADMINISTRATION WITH PROPRANOLOL RESULTS IN INCREASED PLASMA LEVELS OF BOTH DRUGS. THIAZIDE DIURETICS MAY ACCENTUATE THE ORTHOSTATIC HYPOTENSION THAT MAY OCCUR WITH PHENOTHIAZINES. THE PRESENCE OF PHENOTHIAZINES MAY PRODUCE FALSE- POSITIVE PHENYLKETONURIA (PKU) TEST RESULTS. DOPAMINE ANTAGONISTS LIKE PHENOTHIAZINES CAN ANTAGONISE THE EFFECTS OF PIRIBEDIL.