It should not be used concomitantly with medications known to prolong the QTc interval (. 5-HT3 antagonists , tricyclic antidepressants , citalopram , etc.) as this may lead to an increased risk of QTc interval prolongation.   Neither should it be given concurrently with lithium (medication) as it may increase the risk of lithium toxicity and neuroleptic malignant syndrome .    It should not be given concurrently with other antipsychotics due to the potential for this to increase the risk of side effects, especially neurological side effects such as neuroleptic malignant syndrome .    It should be avoided in patients on CNS depressants such as opioids, alcohol and barbiturates. 
In the traditional tests for antipsychotic effect, eg antagonism of stereotypic behaviour induced by dopamine agonists, the chemical groups of antipsychotics mentioned reveal equal but dosage-dependent activity. However, the antistereotypic effects of phenothiazines, butyrophenones, diphenylbutylpiperidines, and benzamides is strongly counteracted by the anticholinergic drug scopolamine, while the antistereotypic effect of thioxanthenes, eg flupentixol is not, or only very slightly, influenced by concomitant treatment with anticholinergics.