Deep sleep, from which patients can be aroused, and coma have been reported, usually with overdosage. Although disturbances such as galactorrhea , amenorrhea , gynecomastia , and impotence have been reported, the clinical significance of elevated serum prolactin levels is unknown for most patients. An increase in mammary neoplasms has been found in rodents after chronic administration of neuroleptic drugs. Because phenothiazines may interfere with thermoregulatory mechanisms, use with caution in persons who will be exposed to extreme heat. Phenothiazines can diminish the effect of oral anticoagulants.
Phenothiazines can produce alpha-adrenergic blockade.
Thiazide diuretics may accentuate the orthostatic hypotension that may occur with phenothiazines. Antihypertensive effects of guanethidine and related compounds may be counteracted when phenothiazines are used concomitantly. Concomitant administration of propranolol with phenothiazines results in increased plasma levels of both drugs. Potentiation of anticonvulsant effects does not occur. However, it has been reported that phenothiazines may interfere with the metabolism of phenytoin and thus precipitate phenytoin toxicity.