Are there any harmful drug interactions between meclizine (antivert) and midol?

No, unless Midol PM: As usual, when taking multiple medications it is wise to keep track of any side-effects that you may experience. Always let your primary doctor know of any over-the-counter medications you are on. That being said, Meclizine and midol should be safe to use together. Make sure it is not midol pm though. That can cause excessive sleepiness that may lead to unfortunate accidents.