<p>Trifluoperazine may diminish the effect of oral anticoagulants. Concomitant administration of propranolol with trifluoperazine results in increased plasma levels of both drugs. Antihypertensive effects of guanethidine and related compounds may be counteracted when phenothiazines are used concurrently. Potentiation may occur if antipsychotic drugs are combined with CNS depressants such as alcohol. hypnotics and anticonvulsant.</p>