Medications to prevent migraine headaches share all the following characteristics EXCEPT?

The characteristic that medications to prevent migraine headaches do not typically share is their universal safety for use during pregnancy. While some medications may be deemed safe for pregnant individuals, others may pose risks, and care must be taken in prescribing during pregnancy.

Preventive migraine medications, such as certain beta blockers, antidepressants, and antiepileptic drugs, have varying levels of safety in pregnancy and need to be evaluated on a case-by-case basis. Thus, not all preventive treatments are considered safe during pregnancy, making this the correct choice.

The other characteristics listed are generally associated with migraine prevention medications. Some medications can indeed reduce the frequency of migraine attacks effectively, and they can also encompass a range of substances, including both preventive treatments designed to decrease the overall frequency of migraines and rescue medications meant to alleviate symptoms when migraines occur. Opioids, while not typically first-line treatments, may sometimes be prescribed for acute migraine pain, making it a less clear-cut characteristic. Hence, option A stands out as distinct from the others regarding general consensus and safety data.