Hello, Irbesartan, diltiazem and meclizine do not have any untoward interaction between them. Therefore no serious adverse event is expected when using them together and you can consider concurrent use as safe. In cases like yours though I usually suggest to my patients to exclude the symptoms being caused by a drop in blood pressure due to the concurrent use of irbesartan and diltiazem (which also decreases the heart rate). If your blood pressure and pulse rate are within the normal range then you can safely discard the suspicion of a side effect and meclizine can be added to the regimen. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Panagiotis Zografakis, Internal Medicine Specialist