Are preventative migraines medication dangerous? long term use?

It depends on the medicine you take. So it is difficult to tell you . Best is to let us know the name or ask the prescribing MD

Medication risk is variable depending upon the specific chemical, and some medications used for migraine do have adverse effects. The more recent CGRP agents appear relatively safe, although severe constipation has been reported in some cases. Have a thorough discussion with your doctor about different approaches, including OTC remedies and choose together.